- For her Earth Two equivalent, see Caitlin Snow (Earth Two). For other uses of "Killer Frost", see Killer Frost (disambiguation).
- "You're not Killer Frost."
- "No. I'm not. I'm something else. And I need to figure out what that is... on my own."
- —Caitlin's decision to Team Flash[src]
Dr. Caitlin "Cait" Snow is a bio-engineer at S.T.A.R. Labs and a former scientist at Mercury Labs. She was working during the particle accelerator disaster and tended to Barry Allen during his coma with Cisco Ramon until he woke up. After he began his crusade as "The Flash" Caitlin became a member of his team with Cisco and Dr. Harrison Wells, before discovering the latter's identity as Eobard Thawne, and provides medical support for the team. Caitlin is also the wife of the late Ronnie Raymond, and is close friends with Cisco, Barry and Felicity Smoak. She is also the former lover of "Jay Garrick", before discovering his true identity as Hunter Zolomon and the former girlfriend of Julian Albert.
In the Flashpoint timeline, Caitlin is not a scientist but is a doctor who is unwillingly brought into Ramon Industries by Barry to help him restore the timeline. Following Barry's attempt to restore the timeline, Caitlin is once again a scientist at S.T.A.R. Labs, but also seemingly from changing time again she is also a meta-human with abilities similar to her Earth Two doppelgänger, who she is afraid of becoming like. However it's also implied that she could have been affected prior to Flashpoint. After being taken over by her rising anger while using her meta-human powers, losing control of her emotions, she briefly started going by her doppelgänger's name Killer Frost.
After suffering a clinical death from a seizure and subsequently being revived by her regenerative powers, her biochemistry was altered, culminating in her becoming fully consumed by her anger as Killer Frost, later encountering and allying with Savitar after the proclaimed speedster god reveals his true identity as a future version of Barry Allen. Later, between Cisco giving Caitlin the choice to cure herself rather than force it on her and watching Savitar nearly kill him, Caitlin finally regained her true personality and control of her powers. Despite this, Caitlin decided not to take the cure. Feeling lost to her own identity, Caitlin left Team Flash on good terms to rediscover herself. Six months later, having seemingly come to terms with her mistakes as Killer Frost, Caitlin finally decided to return to Team Flash, only to discover that her Killer Frost-side had returned.
Shortly after returning to Team Flash, Caitlin once again began to struggle with her Killer Frost side and eventually lost control. Iris West convinced both Caitlin and Killer Frost that they could try to be the same person instead of choosing one life or the other. As such, when preparing to serve as back up to Barry along with Cisco she stated "Snow and Frost standing by" emphasizing that both Caitlin and Killer Frost were prepared to work together to help. When Nazis from Earth-X tried to invade Earth One, she aided her friends in the battle that followed.
From a young age, Caitlin idolized her parents who were both doctors and was inspired to follow in their footsteps. Growing up Caitlin practiced the Hippocratic oath and was obsessed with it. She grew to value life so much she wouldn't even let anyone step on a bug if she could help it. From a young age Caitlin was very close with her father. One Christmas they sat and watched old movies together as it snowed for hours without end outside. However Caitlin's father suffered from multiple sclerosis. Her mother Carla Tannhauser tried to save him as he fought it for years but he eventually died, much to Caitlin's heartache. Following her father's death Carla began focusing only on her work as a way to cope with losing her husband, but her neglect of Caitlin left them estranged for several years.
In adult years Caitlin became a trained neurosurgeon but was still estranged from her mother. Despite being estranged Carla still offered Caitlin a position at Tannhauser Industries but Caitlin wanted to make a name for herself and declined. Some time before 2011 Caitlin was hired at S.T.A.R. Labs by Dr. "Harrison Wells". Sometime after this she met Ronnie Raymond a structural engineer who in contrast to Caitlin's guarded outlook was more outgoing. Caitlin would later describe them as being "Fire and Ice". Despite being very different the two fell deeply in love and started dating. Though she enjoyed working at S.T.A.R. Labs she, like most employees, was often irritated by Dr. Wells' protege Hartley Rathaway.
Around 2012, Caitlin went out of town with Ronnie for their one year anniversary. Before leaving she met newly employed engineer Cisco Ramon after witnessing him debate engineering with Hartley. Cisco and Caitlin became close friends and he would consider her and Ronnie family, as he was estranged from his own and looked up to the couple. Eventually Ronnie proposed to Caitlin and she accepted. However she apparently never told her mother as she wouldn't even be aware Ronnie existed until over 1 year after his actual death.
Particle Accelerator explosion
Caitlin was working on the night that the S.T.A.R. Labs particle accelerator was to be switched on. She and her fiancé, Ronnie, were discussing their honeymoon when they were alerted of the impending switching on. After he switched it on, Dr. Harrison Wells went to make a toast, but it was made apparent that the particle accelerator was malfunctioning. Being the structural engineer, Ronnie had to go down with Cisco Ramon to try to, if not repair it, contain the blast. Despite her hesitation, he had to go. After he didn't come back in a while, Caitlin went down to talk to him. However, Ronnie had had Cisco put the accelerator into lock-down, locking him inside the core chamber. Caitlin and Ronnie talked, but before they could continue, Ronnie's connection was lost, apparently being killed inside the chamber, greatly upsetting Caitlin.
Following an accident involving lightning striking him, Barry Allen was put in a coma. After his situation got critical, he was moved to S.T.A.R. Labs where he was stabilized. Sometime following his move, Cisco, along with Caitlin, met Felicity Smoak during one of her visits to see the patient.
Time in Starling City
A little while later, Caitlin and Cisco were asked to pack up a S.T.A.R. Labs warehouse in Starling City, following the massive explosion that occurred in Central City. The two were doing an inventory count, discussing the particle accelerator's explosion, when they heard movement in the warehouse. They went to investigate, only to find a security guard standing there. Cisco assured him that they were almost done, though he just stared them down, creeping him out. Before the man could reply, he spat blood out and dropped to the ground, with Deathstroke ready behind him. The two made a run for it, managing to incapacitate Deathstroke momentarily with an old energy gun made by Arthur Light. They later reported the incident. Sometime after, they met Felicity Smoak and John Diggle at the hospital. Felicity asked about Barry's condition, and Caitlin told her how it was still the same. Cisco quickly blurted out that "Iris" had been visiting him a lot. When Felicity asked who Iris was, Cisco struggled to explain their relationship, causing Felicity to walk off distressed that "Barry's in a coma, he's already moved on". A little while later, Felicity met the two of them in a lab, with a vial of Mirakuru, telling them that she needed their help and that it would be their little secret. Caitlin and Cisco successfully created a cure to Mirakuru that would be used to cure the Mirakuru soldiers during Slade's seize of the city and cure Roy Harper of his unstable condition.
Working with The Flash
Nine months after he was struck by lightning, Barry awoke from his coma to Lady Gaga's "Poker Face", a song he allegedly liked. Cisco called "Dr. Wells" down to lab as quickly as possible, and explained to Barry what had happened, introducing he and Caitlin. The two took a break as Wells showed Barry around S.T.A.R. Labs, explaining in depth what had actually happened. Later, after discovering that he had the ability to run at super speed, the team of four headed down to an airfield. After Barry commented on her lack of smiling, she admitted that it felt like the best course of action considering what she'd been through. As Cisco monitored Barry's speed, Caitlin measured his energy output, amazed at how fast he could run, before collided with some water barrels. They headed back to S.T.A.R. Labs where Wells and Barry discussed the potential for the existence of other people like him, specifically another who had super speed like Barry, though Harrison was certain that Barry was unique. Barry left to meet Iris. After an encounter with Clyde Mardon's weather manipulation, he returned to S.T.A.R. Labs where he was angry at Wells for lying to him in regards to meta-human abilities. Barry returned later, sorry, offering an apology in return for Cisco and Caitlin's help in catching rogue meta-humans. They agreed to help, and Cisco revealed a suit he'd designed for use by firefighters, which he believed would fit Barry's needs perfectly. Barry donned the suit and headed out to where they pinpointed Mardon to be. Cisco and Caitlin communicated with Barry, giving support. When Barry began to attempt to unravel it, Cisco stated his belief that Barry could withstand the pressure, though Caitlin didn't believe Barry himself would. However, after motivation from Dr. Wells, he eventually did.
After a run-in with a strongman at the Central City National Bank, Barry arrived back at S.T.A.R. Labs with a wrongly-healed ankle, after having previously broken it. They decided to re-break it, and Caitlin suggested to run extra tests to make sure that there was no further damage. Following that, Caitlin and Cisco tagged along with Barry to grab some DNA samples from the crime scene at which the strongman had been. While analyzing the sample, they helped Barry find a group of chimpanzees that had escaped from the Central City Zoo. As he locked them up, they revealed that the DNA sample was that of Joey Rose, a former strongman at the Central City Circus. They delved deeper into the closed circus, discovering that its owner had escaped from Belle Reve and killed several people. They notified Barry of this, while Dr. Wells also provided some details he knew on Mr. Bliss from having attended the circus previously, and Barry left to find the circus. Having been gone for a while, Cisco and Caitlin took a truck and crashed through the tent of the circus. Cisco grabbed Barry and Caitlin attempted to drive away, however their truck was lifted up by Joey Rose, who threw it some distance from the circus tent. As they crawled from the wreckage, they encountered the snake lady. The lady promised to let them pass, but Caitlin believed it to be a trap. The lady assured her that she was genuine, as they were only compliant to Mr. Bliss otherwise torture would be inflicted on them. Before leaving, Caitlin asked what all of it was about, but the woman was only aware that something big was happening. They headed back to S.T.A.R. Labs, where Caitlin explained what had happened to Barry and Cisco further explained what the snake lady had told them. Caitlin suggested that she could experiment with psychotropic drugs on Barry, though she was unsure how he would react. Noticing that Mr. Bliss had arrived at a Central City Cougars match, Dr. Wells urged that they go down to warn everyone. Having destroyed the work van, they took Cisco's car, which Caitlin found unhygienic and tiny. As they arrived, they noticed that The Flash had already evacuated everyone. Iris greeted them and they claimed to be there for the circus.
Caitlin walked in on Cisco as he guided Barry towards a burning building to save people inside. Once he had saved everyone, she ordered him back to S.T.A.R. Labs. Though he tried to justify what he was doing, using his abilities for good, she mentioned that they had actually agreed to locate and contain meta-humans together. Not being able to get her message across, she had Dr. Wells try to help communicate it. She angrily told Barry that she couldn't fix him every time something broke before walking off. After later fainting, Barry headed to S.T.A.R. Labs, where Caitlin yelled at Barry for keeping it to himself, as he could have suffered from a mini-stroke. They decided to test his vitals while he ran on a modified treadmill. They noted his low glucose levels, but not before he fell off and hit the padding. They hooked him up to 40 IV bags in order to bring him back to normal. When he awoke they explained what they determined to be the problem: he hadn't been eating enough for his massive metabolism. Shortly following, Joe appeared through the doors. He began to get angry at Barry for acting as a hero, and Caitlin agreed with his reasoning, before Joe left upset. Yet again Barry later returned to S.T.A.R. Labs, having had a run in with a meta-human who could duplicate himself, who they found to be Danton Black. From some of the perp's blood on Barry's suit, Caitlin was able to speed up the replicating process, making a clone from cells. The clone came to life, freaking Caitlin out, though Joe had returned, shooting the clone. They figured that Danton Black had activated some clones, thus the clone's movement, and Barry suited up to head to Stagg Industries. The team provided support to Barry as per usual, Caitlin suggesting to locate the prime in order to take them all out. Barry ultimately beat Danton, who fell to his death. They soon watched a report about it on the news. Barry assured that the three of them were always with him, and that really all of them had been struck by lightning, not just Barry, at least in the metaphorical sense.
A while later, Cisco and Caitlin alerted Barry to a man with a gun in a getaway car being chased by cops, who Barry sped to and placed in the cop car within a matter of seconds. The following day, after the Darbinyan crime family were gassed to death by a presumed meta-human, the S.T.A.R. Labs team began researching what they could, all of them excited by the potential prospects. Joe noted that they would have to find somewhere to hold them, as Iron Heights was less than ideal, and Cisco suggested the particle accelerator. Not wishing to go down, Barry suggested she tag along with him to identify the poison gas. At the CCPD, they headed upstairs. On the way they were joined by Barry's boss, Captain Singh. Caitlin claimed to be Barry's personal physician. Once they were in the lab waiting for the gas' test results, they discussed Caitlin's late fiancé Ronnie. Once they got the test results, they were intrigued to find two separate tissue samples in it, rather than just one, coming to the conclusion that the meta-human could in fact turn into gas himself, hence why his genetic residue was left behind. Barry left to find the meta-human after hearing news on a police radio, leaving Caitlin at the lab. He eventually found the man, but inhaled some of the gas. He returned to S.T.A.R. Labs where Caitlin used a needle to painfully extract the gas before it killed him. Once he woke up, Barry apologized for leaving so suddenly, but Caitlin reassured him that it was fine and he had just reminded her of Ronnie. Barry related the story of his mother's death, and offered to go into the core chamber with Caitlin to conquer her fears. While they were there, he promised her that Ronnie was a true hero. They were called back up where they were shown the molecular makeup of the poison gas, hydrogen cyanide mixed with a sedative. Barry recalled that executions used those particular chemicals and Caitlin uncovered Kyle Nimbus, who would have been executed at the time of the particle accelerator explosion. She further went on to look up who caught him, Detective West, figuring that he was his final target. Caitlin gave him an antidote to the toxin, and Barry sped to Iron Heights Prison to protect Joe. The team supported Barry, and once he had lured Nimbus out in to the open, Caitlin reminded him not to breath any gas in (as he'd used the antidote on Joe). Finding it too difficult to outrun him, Caitlin suggested to simply have him continue running at Barry to sap his strength, forcing him to revert to human form. Finally capturing The Mist, as Cisco proudly nicknamed him, they put him in the makeshift particle accelerator prison they'd engineered. Cisco attempted to apologize for the night of Ronnie's death, however Caitlin admitted that she was okay, as she was even more proud of Ronnie. The two headed out to the cinemas, followed by ice cream.
Caitlin played Barry in a game of Operation while Barry was also played a game of Chess with Harrison Wells, and a game of Ping pong with Cisco while Barry was testing his ability to multitask. When Felicity arrived at S.T.A.R. Labs, Caitlin was pleased to see her again though she was worried that she would know to much of their operation. Caitlin was told that she wouldn't need to worry after being told Felicity works with The Arrow. After the cold gun was stolen, Caitlin along with Harrison learned that Cisco built a weapon that was powerful enough to stop Barry, despite his speed. After Barry was struck by the cold gun, Caitlin noted that Barry's nerve cells would've been damaged permanently had they not regenerated at the speed they did. When Cisco told Barry he built the cold gun to stop him, Caitlin defended Cisco that he was only taking precautions and that it was when Barry was still in a coma. Caitlin was later shocked when Felicity managed to track down Leonard Snart/Captain Cold in a matter of seconds. When Caitlin and Cisco were advised by Felicity to follow Barry and help him, Caitlin reminded Felicity that Barry wanted to be alone. Caitlin was told by Felicity that when someone asks to be alone, that is the best time to help them. Caitlin, along with Cisco and Felicity brought the S.T.A.R. Labs vacuum cleaner, claiming it was the prototype cold gun four times more powerful than the one Leonard had to threaten Snart into backing down.
Barry took Caitlin and Cisco to a social gathering with Iris and Eddie Thawne, who she expressed an attraction, but Barry told her he couldn't get drunk so she took a sample of his blood in a syringe, which she kept in her bag, but Barry was soon called to a bombing in a building where a man was hanging for his life. Later Barry went to find the bomber Sgt. Bette Sans Souci but returned moments later without his suit, after Caitlin desperately tried to get back in contact with him over communications, stating that Bette destroyed it causing it to explode with a single touch. Flash managed to bring Bette back to the lab where Caitlin was able to figure out that the dark matter of the particle accelerator merged with a piece of shrapnel where she got her powers, and later observed as Bette tested her powers. Bette told everyone that she was being targeted by her commanding officer Gen. Wade Eiling and Caitlin tried to find a way to remove her powers but discovered that there was no means of reversing it and though Barry wanted her to stay, become a member of the team, everyone including Caitlin feared she would eventually unintentionally destroy the lab and they needed to avoid being Eiling's enemy. After Bette was killed by Eiling, Barry became slightly depressed and Caitlin tried to cheer him up by making note of his power to walk on water and later made an whisky shot strong enough for Barry to feel.
As Caitlin and Cisco debated how many insects Barry swallows while running, Barry came to S.T.A.R Labs with a broken hand caused by meta-human Tony Woodward, Barry's childhood bully, which Caitlin tended to but noted that 13 bones were broken in his hand alone, in addition to multiple injuries in the rest of his body. She later watched as Barry practiced fighting on a robotic dummy and dislocated his shoulder and Caitlin tried to fix it but when she asked if Barry was visiting Iris as the Flash again, he lied promoting Caitlin to fix his shoulder by brutally snapping it back in place with her hands. Caitlin and Cisco later deduced where Tony was hiding out, but when Barry was seriously wounded Caitlin and Cisco had to go find him themselves and bring him back to the lab. Cisco and Dr. Wells both agreed that Barry could defeat Tony if he hit Woodward at just the right angle at a speed just over Mach 1, which would require a clear shot 5.3 miles away from his target. Caitlin on the other hand begged him not to as it would shatter every bone in his body if done wrong. Later Barry engaged Tony again after the latter had kidnapped Iris, and after getting hurt he ran out, only to stop 5.3 miles away from Woodward, turn around and run at a minimum speed of 837 miles per hour, which Caitlin begged him not to do but nerveless he succeeded. Caitlin watched as Barry confronted Tony, face to face, and was amused by Cisco's desire to stop his own childhood nemesis next.
When Caitlin was walking in the parking lot after she met up with Jason Rusch to learn more about F.I.R.E.S.T.O.R.M., she was kidnapped, due to her association with The Flash, by Leonard Snart and Mick Rory before she could get into her car. She was later rescued by Cisco and Joe West.
The team learned of Eobard's plan, to have Barry run fast enough to create a wormhole in which Eobard could return home while Barry could save his mother from Eobard in the first place thus restoring the timeline to order. Caitlin thought the concept was an easy choice until Professor Stein elaborated that Nora's murder had subsequently altered the timeline and changed history, so therefore nothing would ever be the same and no one would know because they'd never remember it, meaning Barry may never meet any of them. After tending to Ronnie's wounds from his battle with Reverse-Flash he told her that he and Stein are there to stay for good, and asks if she would like to finally marry him and she said yes. Later the two decided to marry before Barry time-travels in case everything does change and they, with Professor Stein as their rabbi, said their vows and married. When Eobard was to travel back to the future Barry surprisingly returned and sabotaged his time sphere, forcing Caitlin and Ronnie to manually turn off the generators to close the wormhole before it could grow into a singularity. They succeeded, but, as a result of a paradox from Eddie killing himself to erase Eobard from existence, the wormhole reopened, and the team was helpless to watch it grow and begin consuming everything in Central City before it would eventually consume the world. Flash sped off into the portal to close it  and managed to stabilize its range but wasn't able to close it. Professor Stein informed Ronnie the only way to destroy it would be for them, as Firestorm to separate inside it. Caitlin immediately protested but Ronnie professed that they have to try and kissed her farewell, before becoming Firestorm and flying into the singularity as Caitlin watched in tears. Though Firestorm succeeds in destroying the portal Ronnie doesn't survive and is presumed killed inside the singularity, much to Caitlin's devastation.
Working at Mercury Labs
After Ronnie's death Caitlin held herself responsible remembering Ronnie's offer to leave Central City months earlier, and kept thinking what might have happened if she'd said yes but she did not blame Barry despite his assumptions.
Soon after she was employed by Dr. McGee at Mercury Labs as being at S.T.A.R. Labs reminded her too much of Ronnie, and subsequently had little to no contact with the rest of her friends. 6 months later she did however briefly attend the "Flash Day" festival. Cisco later visited her and asked her to run a DNA sample off their meta-human suspect, dubbed "Atom-Smasher" by Stein, and she reluctantly agreed. Later Barry visited her and revealed that Eobard had made a video message in the event of his death but was too afraid to watch it, so Caitlin offered to watch it with him. In the message Eobard confesses to Nora's murder much to their shock and delight, and Caitlin decides to rejoin the team and help them defeat Atom-Smasher.
After defeating him, Caitlin and Cisco see to it that S.T.A.R. Labs security is increased but as they are informing Barry of this, a stranger walks right in and introduces himself as Jay Garrick and tells them that their world is in danger. Jay reveals he knows the names of everyone present, Caitlin included, and explains that he is from another earth, Earth Two, and more shockingly reveals he is a speedster himself named "The Flash" and was unwillingly pulled brought there as a result of the singularity as he battled another speedster named "Zoom", the same man who sent Atom-Smasher to kill Barry. Jay however lost his powers when he arrived and spent the last 6 months gathering information on Team Flash but a skeptical Barry asked if he'd run tests to confirm he is a speedster, which he accepted. Caitlin ran these tests and learned that Jay acquired his powers through similar circumstances to Barry, but Caitlin was quite taken to learn he was also a scientist. Caitlin learned that he did have regenerative capabilities but no evidence he has connections to the Speed Force, but also ran a polygraph on him without his knowledge which came back positive. Caitlin ran further tests on him on the treadmill where she seemed to have developed an attraction to Jay, though she quickly denied it when Iris implied that Caitlin had feelings for Jay. This is further implied when Jay reveals moments later that Caitlin ran a full body scan on him at her request, and she claims she was "being thorough". Caitlin and Cisco later watched Oliver's broadcast on Star City news where he re-declared himself as the "Green Arrow", and Caitlin approved of Oliver's new name but Cisco didn't. After defeating Sand-Demon Caitlin tended to Jay's wounds and he complimented her skills and as he reflected on the loss of his powers, she also told him she'd lost something precious to her too (Ronnie) but eventually learned to live with it and they exchanged smiles. After Professor Stein confirmed the presence of multiple ruptures in the city, 52 exactly, he collapsed and Caitlin tended to him.
Seeking to use Turtle's powers to stop Zoom Caitlin and Jay went to check on him but discovered him dead in his cell. Jay was quick to blame Harry but he denied it though Caitlin, like Jay, was unconvinced. After discovering Jay's declining health Caitlin theorizes that a fresh infusion of healthy cells could fix Jay's blood, by finding his Earth-1 doppelganger. Caitlin asked for Barry's help but he was unable to find any Jay Garrick on Earth-1. Caitlin decided to ask Jay himself but after telling him he didn't have an Earth-1 double Jay claimed there was a good reason and asked her to meet him at a park where she'll see for herself. Later when Caitlin and Jay sat down at the park Jay revealed he too tried to find his Earth-1 double but with no success, at least at first. After some time however he eventually did find his doppelganger and pointed him out on a bench across the park, Hunter Zolomon. Caitlin questioned why Hunter had a different name to Jay and he told her his mother died in childbirth, and after bouncing around different families was adopted by the Zolomons. However, Jay told Caitlin that his cells were mutated after becoming the Flash, and Hunter's cells were no longer compatible.
While Cisco was using his powers trying to locate Zoom he discovered that Reverse-Flash was still alive and invading Mercury Labs. However when Barry returned from his encounter with the speedster he stated Eobard didn't know his name or that they've fought before. Harry theorized correctly that this version of Eobard is a younger version of the man they knew, one who has not yet traveled back to kill Nora and is meeting Barry for the first time. When Barry captured Eobard but wasn't allowed to talk to him because he would alter the timeline, Caitlin tried to reassure him to take comfort in the fact that he caught him. Barry however wasn't satisfied. When Cisco started seizing Caitlin stabilized him but he started fading out of existence to which Harry surmised was a result of Eobard's capture, rupturing the timeline and Barry was forced to send him back.
When Barry, Cisco and Harry went to Earth-2 to rescue Jesse the Speed Cannon malfunctioned and Jay timely saved her from being crushed under one of its rings when it fell apart. As Caitlin and Jay tried to repair it Joe told them of a metahuman Adam Fells/Geomancer, attacking the city looking to challenge Barry. Though they didn't have Barry Joe pointed out that Jay got his speed back with Velocity-6 long enough to save Harry, but Jay refused to take it. Caitlin confronted Jay on his hesitance and he admitted that he had taken the Velocity serum prior to Caitlin perfecting it, out of selfishness for wanting to increase his speed. Caitlin then quickly realized that taking the Velocity serum was the true cause of Jay losing his speed, not Zoom, and Jay admitted he'd made so many mistakes and wasn't worthy of Caitlin's love. However Caitlin reassured Jay she'd figure out a way to restore his speed and save him and worked on perfecting the formula, and created Velocity-7. After doing so Flash went out to stop Geomancer but during their fight the Velocity-7 wore off, and Flash was almost killed by Geomancer but Joe was able to save him. As Caitlin tended to Jay's wounds she promised that Velocity-8 would be better, but expressed worry that Barry, Cisco and Harry wouldn't make it back in time.
While working on Velocity-9 she discovered a flaw in its cellular matrix and visited a friend at Mercury Labs, Eliza Harmon, who helped her finish the formula, though Caitlin was careful and only gave her specific aspects so the formula couldn't be replicated in case Eliza's research was compromised. After this Caitlin was finally able to perfect the formula to Velocity-9 just in time for Geomancer to cause an earthquake that, destroyed a hospital. Before it collapsed Caitlin was forced to give Jay toe formula before testing it and Flash was able to save the people inside before it collapsed. After returning Caitlin and Iris stood in awe of Jay's achievement and Caitlin was happy to see she succeeded, and also discovered that Velocity-9's effects had begun to fix Jay's cells. As Caitlin called Jay to inform him of this however she and Iris were confronted by Geomancer in S.T.A.R. Labs, and attacked them. However Caitlin was able to save Iris by using the B.O.O.T. on Geomancer, and Joe ensured Fells was arrested. When Jay did return she informed him of the Velocity-9's effects on his cells and Jay was speechless, unable to express gratitude in words so Caitlin kissed him instead. Almost immediately however they discovered the Speed Cannon was damaged in Geomancer's attack, but Flash and Joe were able to stabilize it. After Barry, Cisco, Harry and Jesse returned Jay closed the last breach but before it closed for good, Zoom appeared and stabbed his arm though Jay's chest killing him and pulled him back through the portal, right in front of Caitlin. Moments after Caitlin was shell shocked and started repeatedly saying "he's not dead" much to everyone's concern, until Cisco helped her and she tried sleep it off.
Following Jay's death Caitlin went into depression and tried to hide her feelings but became quite snipping and blunt, much to Cisco's concern. While the team were helping John Diggle and Lyla Michaels capture King Shark Cisco confronted her about her cutting off her emotions, but accidentally revealed he met Caitlin's Earth-2 doppelganger. After Caitlin confronted Cisco on the subject he confirmed he had met Earth-2 Caitlin, who was a meta-human named "Killer Frost" and a murderous criminal, and Cisco expressed worry because Caitlin was starting to act just like Killer Frost with her demeanor. However Caitlin stated that if she let herself feel the grief of losing Jay she'll never recover and she can't, and insisted they get back to finding King Shark. After King Shark was captured Caitlin pranked Cisco by pretending to be Killer Frost which terrified Cisco, until Caitlin started laughing. Caitlin then reassured Cisco that she may be depressed but she'll never be like Killer Frost, and watched as Barry revealed the display for Jay's helmet and vowed to find a way back to Earth-2 to beat Zoom.
While enjoying a night out at a dance club Caitlin and Cisco danced while Barry, Iris, Wally and Jesse watched but the club was attacked by another speedster, Trajectory, and Caitlin suspected the speedster was using Velocity-9 and told Barry about it. However Barry was furious to learn Caitlin had the means to increasing his speed the whole time, but Harry defended her as Jay had previously stated how dangerous the drug was. After Barry fought Trajectory Caitlin suspected she may be Eliza but when she and Joe questioned her about the research Caitlin gave her, she revealed she destroyed it after helping her and Eliza checked out. However the team was attacked by Trajectory who locked Flash in the pipeline and revealed she was indeed Eliza, demanding more Velocity-9 and threatening to kill Jesse. After succeeding Trajectory injected Jesse with Velocity-9 and escaped and saved Jesse by giving her a transfusion of Harry's blood. After Trajectory killed herself by accidentally overdosing on Velocity-9 Barry revealed that before she evaporated her lightning turned blue, just like Zoom's. With this knowledge Harry deduced that Zoom is dying and needs a cure which is why he wants Barry's speed, and Barry pointed out that Jay too was dying. Caitlin immediately denied the possibility that Jay was Zoom but Barry had Cisco vibe Jay's helmet, and he shockingly confirmed that Jay is Zoom.
After Barry and Harry created the tachyon enhancer based on Eobard's information, Barry was able to run four times faster, faster than Zoom, and realized he could take him down now. After Cisco figured out how to open breaches Barry prepared to fight him, telling Caitlin she doesn't need to partake if she doesn't want to. Caitlin however stood firm that she needed to help them stop Jay, whatever his real name is. When Barry questioned what she meant she revealed that Jay's doppelganger's name was Hunter Zolomon but Harry was astounded, as Hunter Zolomon on Earth-2 is a serial killer, convicted on 23 counts of murder. After showing a newspaper of him the team realized that Jay was actually Hunter but Barry used this information to their advantage to set a trap for him. Barry successfully lured Zoom into their trap, using cutouts of the Earth Two versions of his parents to catch him off guard, but he still escaped and abducted Wally. After agreeing to Zoom's deal to release Wally in exchange for his speed Zoom brought Wally back and unmasked in front of them, revealing his true self for the first time. While Harry prepared the device to drain Barry's speed the team questioned how Hunter was still alive, as he'd died and he revealed he'd brought a younger version of himself to the present to act as his decoy, ultimately to sacrifice him to motivate Barry into becoming faster. He also admitted he'd posed as The Flash to give people hope only to take it away from them, and Caitlin openly called him a monster. After Hunter successfully drained Barry of his speed he tried to kill him but Caitlin begged him, asking if he ever truly did care for her, if he has any humanity left to let Barry goes. Reluctantly, Hunter did so, but seeing Caitlin as a weakness he couldn't let go, Hunter abducted Caitlin and took her back to his lair to Earth Two.
While imprisoned in his lair Hunter acknowledged that Caitlin was mad at him for lying to her but told her that he loved her, much to her terror and allowed her to roam free knowing she couldn't escape and tended to other business. While venturing she discover a man in an iron mask using tap code against his cell, but Caitlin couldn't understand. Caitlin was then distracted by her doppelganger Killer Frost who was imprisoned in the opposite cell. Frost immediately mocked Caitlin's choice of clothing and didn't know who the iron mask was either, nor did she know why Zoom had imprisoned her. However Frost made a deal with Caitlin that if she got her out of her cell she'd get her back to Earth One. While working on a means to break the carbine in the cell the Caitlins talked about their very different upbringings but found common ground in their shared dislike for their mothers. However Caitlin Two revealed her mother was a frigid narcissist because her brother Charlie died, though Caitlin One never had a brother nor did she know why her mother was cold. After freeing Frost she immediately betrayed her and tried to kill her revealing the only reason she's still alive, is because she looks just like her, the woman Zoom loves and therefore wouldn't need her anymore. However before Frost could kill her Zoom returned and phased through Caitlin, literally, to grab the icicle Frost made and stabbed her with it, horrifying Caitlin and leaving Frost to bleed out. Hunter then threatened to kill his masked prisoner if she tried to escape again. Later Caitlin tearfully pleaded with Hunter to let her go and Hunter agreed, as he sought to conquer Earth One. Zoom then took him with her back to Earth One.
Returning to Earth One, Caitlin became a witness to Zoom's ruthless conquest of Central City Police Department. As he killed policemen and "failed" minions without mercy, Caitlin pleaded Hunter to stop this madness. Annoyed at her demeanor, Zoom encouraged to embrace darkness instead, and threatened to kill her friends next if she didn't stop meddling in his business. Eventually, Hunter presented Caitlin with a choice: stay with him, and become the queen of his meta-human empire, or leave, and share the same fate as the rest of Team Flash. As Zoom left Caitlin to address the meta-humans under his command, she escaped back to S.T.A.R. Labs Seeing her lover's merciless side took a toll on Caitlin's mental health, as she started hallucinating, seeing an apparition of Zoom appear behind her friends in S.T.A.R. Labs. Refusing to meet Hunter in person, Caitlin nevertheless agreed to act as bait for him via hologram, telling that she accepted her inner darkness, just like he wanted her to. Hunter rejected her "reconciliation", and tried to swipe at her legs, only to discover that Caitlin was but a holographic projection. He was then overtaken by Team Flash, but not before taking Joe West with him to Earth Two. After Zoom's race against Barry and his imprisonment in the Speed Force by Time Wraiths. As Barry explained how he used a time remnant to beat Zoom they awaited for Cisco and Harry to free the man in the iron mask from his predicament. Much to their shock however the man was the real Jay Garrick who was also Henry's Earth-3 counterpart. After Jay reclaimed his suit he further decided to take Hunter's helmet as a means to inspire hope whereas the helmet was meant as a symbol of false hope. Caitlin complimented Jay that it suited him. After Harry, Jesse and Jay returned to Earth-2 Caitlin attended a celebration of victory over Zoom, when Barry made a choice to alter his parents' fate, creating a "mirage" timeline known as Flashpoint.
Return of Killer Frost
Whether as the result of Flashpoint or not, Caitlin developed cryokinesis meta-human powers akin to those of her Earth Two counterpart. She kept this a secret from the rest of the team, using them to help Barry escape Mirror Master's mirror trap. However, she later noticed while taking a shower that some of her hair turned pale blonde; she promptly cut off the altered hair to hide her powers. Desperate to understand what was happening to her, Caitlin visited her mother but was quickly annoyed when she asked if Caitlin had received her birthday card which she confirmed, in April, presumably a significant amount of time before or after it. Caitlin inquired how to get an appointment with her for a friend, not ready to reveal her secret, but as Carla coldly walked her through the procedures Caitlin angrily froze her desk and revealed she was the patient. Carla subsequently canceled all her appointments for the day and readied various tests for Caitlin. While preparing she met Carla's assistant Nigel. Caitlin was brought down to the facility's testing lab for molecular motion where she revealed a shaft made of solid tungsten, heated to over 2000 degrees centigrade. Carla asked Caitlin to freeze it in order to determine how to reverse what's happening to her. To her horror she froze it solid within seconds. After Caitlin revealed the origin of her powers, she and Carla fought over Caitlin working at S.T.A.R. Labs rather than Tannhauser Industries, which Caitlin reminded her was because she desired to make a name for herself. Before they could argue further Nigel came back with the results and revealed that Caitlin had not just frozen the tungsten but had absorbed all the energy it was emitting. However Caitlin was frustrated when she heard them talking about how her power could benefit their pursuits rather than offer sympathies. When Carla began taking blood samples Caitlin, finally having had enough, confronted her over he seemingly lack of care for her well-being and how she hasn't expressed any concern over her well being since her father died. Carla defended that she tried to save him and reminded Caitlin that she ran away but Caitlin told Carla that she had to because she wouldn't even so much as look at her. Carla accepted Caitlin's anguish and admitted that she got consumed in her work out of grief but scolded Caitlin, believing she didn't know what that kind of loss feels like. Outraged, Caitlin told Carla about Ronnie, who Carla didn't even seem to be aware of.
Having had enough, Caitlin decided to leave but Nigel trapped her in the facility wanting to exploit her powers for himself. As he grabbed her Caitlin's inner Killer Frost persona was released in a fit of pure rage and she grabbed Nigel and froze his arm solid. Carla came into confront her, and Killer Frost ordered her mother to move, but Carla offered her apologizes, acknowledging that she wasn't much of a mother, but was steadfast that she didn't raise a killer, managing to talk her out of killing Nigel as mother and daughter hugged. Caitlin returned to help Team Flash stop the supposed monster roaming the city, only for it to be a hologram. Caitlin later told Cisco about visiting her mother and he commended her for trying to make amends with her family. Later Carla contacted Caitlin via webcam and told her that her results proved unfruitful; that Caitlin's biology was rapidly changing and the more she used her powers the less control she'd have. After hearing this, Killer Frost's anger emerged again, as Caitlin has accidentally frozen her computer, horrified to see that she was losing control over her emotions along with her growing meta-human powers. Worried of her powers, Caitlin stole power dampeners from S.T.A.R. Labs, something that Cisco thought to blame on H.R. Wells. She was seen wearing the dampeners during an attack of the meta-human Shade. After Cisco accidentally vibed Caitlin in the guise of Killer Frost, he forced her to reveal the truth about her powers to the team.
Caitlin said she wouldn't save Barry from Savitar, for fear of using her powers and unleashing her Killer Frost side, and only went after Iris begged her. And after using her powers to save Barry from Savitar; unfortunately, she ended up dominated by her worry and anger, turning into Killer Frost. She went after Dr. Alchemy in an attempt to rid herself of her powers. She tricked Joe into believing that Wally has emerged from his cocoon, trying to divert Joe from the interrogation of one of the acolytes of Alchemy. She tortured the acolyte, but before she could extract any useful information, Caitlin was forced to flee by approaching CCPD officers, leaving the acolyte frozen. Still obsessed with finding Alchemy, Killer Frost kidnapped Julian Albert, forcing him to create a search algorithm to find Savitar's acolytes. Julian succeeded in locating a member of Alchemy's cult, but also alerted the police to Killer Frost's location, as she tried to kill him. However, The Flash arrived and attempted to talk Caitlin down, even knocking out Albert to permit them to speak freely. Unfortunately, Caitlin was unable to control her powers; too far gone and panicked, she stabbed him in the leg and went after one of the acolytes, Craig. Upon arriving, she threatened the man's family, forcing him to comply. He informed Killer Frost that he didn't know where Alchemy was, or who he was, but only that Alchemy was merely another acolyte of Savitar who had shown them the future where, among other things, Caitlin had become Killer Frost. However, before she could press for more info on how to take away her powers, Vibe arrived and, like Barry, attempted to talk her down, but Killer Frost attacked Cisco. Barry then arrived on the scene and knocked Killer Frost to the ground. Unwilling to surrender, Killer Frost gave Barry a kiss, using her powers to freeze him solid. Luckily, Cisco was fast enough to smite her with a Vibe burst, knocking Killer Frost unconscious. Upon waking up in the Pipeline, Killer Frost attempted to convince Team Flash she was back to normal, to no avail. She then made an offer of leaving them alone, if they release her and allow her to go on her way. But Barry refused to abandon her, angering Frost. She yelled at him, blaming Barry rightly for everything bad that happened to the team after Flashpoint. Barry returned, asking for Caitlin's help with a freed Wally West, who couldn't maintain control over his powers. Killer Frost taunted Barry, who released her on one condition: if she wanted to leave, she had to kill him. Killer Frost threatened to do so, producing an icicle, but was unable to kill her friend. Crying, Caitlin finally snapped out of her anger and she hugged him, horrified at her actions. Barry comforted her and she went back with him, assisting the team in returning Wally to normal (albeit now with Super-Speed). Barry quit his job to save Caitlin from a life in prison after pleading with a furious Julian Albert, who would not be swayed to keep her secret unless Barry resigned from his work as a CSI, and she never thanked him for this.
During a joint mission with the Legends to stop the Dominators' invasion, Caitlin mostly partnered up with Professor Martin Stein, who encouraged her to learn how to control her powers, instead of denying them, just like he did as Firestorm. On her end, Caitlin helped Professor Stein to accept his daughter, Lily Stein, who was born as a result of an accidental temporal aberration.
After the Flash has defeated Alchemy and took the Philosopher's Stone to S.T.A.R. Labs safe in its compartment box, Savitar tried to manipulate Cisco Ramon into taking the stone for himself and releasing him, appearing to Cisco in the guise of his late brother, Dante Ramon. Despite being threatened by Cisco not to approach him, Caitlin managed to talk him down and persuade to hide the Brahmastra, stopping Savitar again. Later on, Caitlin was present when Team Flash communicated with Savitar, possessing the body of Julian Albert. She was worried as he claimed a prophecy for Team Flash, saying that one of them would fall, the other betray them, and the other would suffer a fate worse than death. After this ordeal, Caitlin encouraged Julian to come celebrate Christmas together with Team Flash at West house, later on congratulating the CSI specialist when he came to the party after all. Showing Cisco that she took Martin Stein's advice to heart and started to practice control over her powers, Caitlin removed her power dampener and produced an icy mist with her hand, turning a raincloud above West house into a cloud of white snow.
Attack on S.T.A.R Labs
A mysterious future villain of the Flash named Abra Kadabra appeared, stealing from several tech companies in an attempt to build a timeship to return to the 64th century. Abra Kadabra soon found himself chased after by the Flash and Gypsy, escaping, but not before telling Flash that he knew Savitar's name.
Sometime later, he teleported into S.T.A.R Labs and ambushed Caitlin, Julian and Joe West, but was soon apprehended by the Flash and locked up in the Pipeline, taunting the team about his knowledge of Savitar. There, he told Joe that if he let him escape from Gypsy, he promised to reveal Savitar's name so the team could save Iris. Joe agreed, and set him free, but Kadabra betrayed him, claiming that the terms of the agreement had changed. He then went to collect a mysterious future power source from the Time Vault, and set off an explosive as the trio attempted to chase after him upon his escape. The resulting explosion impaled Caitlin's side with shrapnel. Team Flash took her to the med bay and helped her onto the bed. Caitlin showed signs of physical pain, as she was breathing heavily and moaning. Cisco tried to stop the bleeding with a T-shirt while the team decided how they was going to help her. Julian X-rayed her and found she had bits of metal wedged inside her that needed to come out. Caitlin refused to go to the hospital as they will find out about her Killer Frost identity. Iris told the team that Caitlin couldn't operate on herself but Caitlin said she could if she had a mirror, she could talk someone through the surgery. Soon after Caitlin talked Julian though her own surgery. Iris helped stop the bleeding as Julian operated. As Julian came to the last piece of metal he found that it was stuck, as he tried to get it out, Caitlin's heart rate began to increase dangerously, causing Cisco to worry. Julian told her it was going to hurt as he pulled the metal out, Caitlin screamed in severe pain before becoming light headed and telling Julian to stitch her up as she was going to pass out. Not too long after she woke up in the med bay bed with Julien holding her hand. Julian told her how brave he thought she was before getting up to kiss her, but pausing out of fear of hurting her. Later that day, Cisco was alone with Caitlin. She seemed to be recovering well, but as they were talking, Caitlin stopped mid-sentence and passed out. She started seizing. Cisco panicked and called for help. Julian came running in with H.R. and they tried to hold her down, but she suddenly stopped. Cisco put his hand above Caitlin's mouth and found that she wasn't breathing. Julian began giving her compressions and told Cisco to get the oxygen mask and place it over her mouth. They then tried electric shock, but everything was unsuccessful. Julian tried more compressions while Cisco continued giving her oxygen but Caitlin wasn't responding and they couldn't resuscitate her. Cisco started crying, realizing his best friend had died. Julian, distraught, ripped off Caitlin's necklace, hoping her meta-human powers could regenerate her. About 30 seconds later, she began breathing again. Caitlin's wound also healed instantly, but she emanated a cloud of mist, sending the team and herself flying. Once the cloud cleared, Caitlin had transformed into Killer Frost and attacked the team.
Alliance with Savitar
After her escape from S.T.A.R. Labs, Caitlin wandered around in the snow, only to encounter Savitar. She asked if Savitar wanted to cure her, to bring Caitlin Snow back, but the armored villain wanted just the opposite. Caitlin then asked Savitar why should she trust him. To prove that he can be trusted, Savitar removed his armor and revealed himself as a future version of Barry. Seeing that, Caitlin agreed to do anything he wants.
She was sent by Savitar to the Central City University in order to kill future physicist Tracy Brand, however her attempt on the scientist's life was thwarted by the intervention of Barry and Cisco. She returned to Savitar to tell him of her failure. Savitar questioned Frost's loyalty by pondering the idea that there may be more Caitlin Snow still within her than she led him to believe, especially due to the fact that despite taking up the name Killer Frost she had not yet actually killed anyone. He then told her to once again try to kill Tracy with the promise that if she succeeded they could both be gods.
A few hours later she kidnapped Cecille at the West house and told Joe that the only way to spare Cecille's life would be to trade her for Tracy. At the site of the trade off she battled both Barry and Cisco before being overcome by Cisco's powers and knocked unconscious. Cisco then acquired a blood sample from her that Julian hoped could be key, due to Caitlin undergoing a full mutation into Killer Frost, to reversing the process and cure their friend. Before the team could return to Star Labs, to presumably lock Frost away in the Pipeline for their and her own safety, Savitar appeared and escaped with the still unconscious Killer Frost.
When Savitar lost his memory, Killer Frost realized that Team Flash erased Barry's memory to prevent the future Savitar is trying to create; but this also caused Wally to lose his powers. She offered them the hard choice of returning Barry's memory or leaving Central City vulnerable to attacks by meta-human criminals. Cisco encouraged her to remember being Caitlin Snow, which allowed her to help restore Barry's memory in surgery. She prepared to leave, with Julian confessing that he had fallen in love with her. This news briefly shocked Killer Frost, who coldly told the entire team she never loved them. When in the elevator, her eyes briefly returned to normal, showing that Killer Frost could be turned back into Caitlin.
Killer Frost was later seen talking to Savitar about his plans if he's really ready to end his former lover's life. He then stated that "It's either her or me", and that when the time comes she should be ready to do her part. When Savitar captured Iris HR Wells risked his life to stop him he switched appearances with her, so when Frost attacked them she didn't realize that she was actually taking back HR. Caitlin then met Vibe in a snowy forest area and said that she needs to "cure herself of Caitlin" and the only way to do that is to kill him. As the fight went on Killer Frost gained the upper hand. Right before Frost could finish off Cisco, Savitar appeared and stated she should keep him alive, as he needs him to modify the Speed Force Weapon. Later on, after Vibe finished making the modifications, Savitar ordered Caitlin to kill Cisco, which she tried to do, but Gypsy interfered and the two escaped.
Killer Frost then helped Savitar kill Black Flash, and then used the weapon on the God of Speed. While interrupted by Team Flash, she took on Gypsy and Vibe but was subdued. Cisco then offered Killer Frost the choice to use the cure and become Caitlin again or remain in her current state. When Savitar attacked Cisco and attempted to kill him, Killer Frost, without using the cure, managed to take control of herself and let go of the mad persona. She attacked Savitar and watched his defeat by Barry and Iris. Caitlin later attended the funeral of HR Wells, where she met Julian and Cisco. She told them about her decision to leave, in the hope that she can rediscover herself. They bid each other goodbyes, and departed on good terms.
Rediscovery and return
Trying to find her own way in life, Caitlin left Team Flash and journeyed away, trying to stay undetected. Staying low profile, she didn't use her many doctorates to get a high paid job, but worked as a waitress in a bar instead. During her stay away from S.T.A.R. Labs she was contacted by Norvok, a member of Amunet Black's organization, and worked for them. During Samuroid's attack on Central City Cisco vibed Caitlin's location and visited the bar she worked in. She smirked at the thought of Barry still being stuck in the Speed Force. Cisco managed to convince her to return back to the team, where she helped Cisco in locating and later diagnosing Barry. Rejoining the team, Caitlin worked on helping to get Barry back to sanity, including using the speedster weapon to stop his mad rampage. Reuniting with Barry, apologizing before Joe and trading banter with Cisco, - all of it influenced Caitlin into leaving her job and coming back to S.T.A.R. Labs. She informed her associates at the bar about her decision to leave and was confronted by Norvok, who tried to strong-arm Caitlin into staying, threatening her for not listening to Amunet's orders. Angered by such an attack, Killer Frost used her meta-human powers to intimidate Norvok, nearly killing him via brain freeze. She was riled up enough to go "have some fun" on a rampage, but managed to force herself out of the violent mood, restoring her hair and eyes back to their natural color.
According to Craig, a member of Savitar's cult, Caitlin would have been described as being "glorious and powerful", and Savitar had "special plans" for her, which did come true as she helped him and he needed her to freeze Black Flash. 
In a news report on a television reporting the arrest of Jared Morillo that Barry saw during his accidental trip to May 2017, a subheading reads "Killer Frost still at large".  While Barry succeeded in altering the circumstances of Morillo's arrest, with Wally defeating him instead of Barry in January instead, Caitlin's future remained the same. Barry later reveals to Joe that Caitlin's on the loose and they need to bring her in, prompting him to alert the CCPD. This causes the aforementioned headline.
When Barry visited a possible future, in the year 2024, it is revealed that Caitlin allied herself with Savitar. Moreover, during the aforementioned battle, Vibe's arms were frozen and shattered by Caitlin, forcing him to replace them with bionic arms and subsequently making him unable to use his powers. Caitlin, still as Killer Frost, has been locked up in Iron Heights, and still refuses to divulge the identity of Savitar, with Julian as her caretaker.
Caitlin is very intelligent and passionate about her work as a bio-engineer and scientist, even keeping a blood collection kit in her purse. She is generally a very compassionate and caring woman. She loved her fiancé Ronnie Raymond very much, he knew how to make her laugh and was devastated by his death which sent her into a state of depression for almost a year, because of this she didn't smile much. However. since being brought onto the team, working with Barry Allen, helping people and saving lives, she has started to liven back up. She has shown great concern for Barry as she often advises against engaging meta-humans they know little about and was initially against Barry using his powers as a guardian angel for Central City, though she eventually grew to accept and even participate in it.
Caitlin is also seen to be somewhat "guarded", in her own words, and timid as seen when she was terrified of going into the S.T.A.R. Labs particle accelerator it being the location of Ronnie's supposed death, though she later overcame this obstacle with Barry's support, becoming more assertive, brave and confident. Despite them being quite different in personality, she is also close friends with Cisco Ramon but finds his need to nickname every meta-human they face annoying, although she has occasionally nicknamed a meta-human now and then herself. Leonard Snart considers Caitlin to be "uptight", which his sister agrees with. When Caitlin was reunited with Ronnie, alive and well after he was separated from Martin Stein, she was overjoyed, no traits of her initial depressive, forlorn personality remaining. When she finally marries Ronnie, she is perfectly content accepting that everything she's experienced over the past year, leading up to wedding the man she loves has been worth it. When Caitlin loses Ronnie again, this time for real, Caitlin is devastated, so much she is unable to stay in S.T.A.R. Labs as she blames herself for his death. However she has slowly managed to recover and regained her desire to help Team Flash.
Though not as prominent as her other traits, Caitlin has a somewhat flirtatious side to her personality. Often when flustered or uninhibited by the effects of alcohol she can become silly, frazzled, and hinted a few times during her night out at the dive bar with Barry that she dropped many hints that she was interested in Barry. After meeting Hunter Zolomon, masquerading under the name "Jay Garrick", he and Caitlin have quickly become infatuated with each other, their infatuation developing into a relationship. Caitlin's love for Hunter was the driving force for her to find a cure for his condition. However, after the revelation of "Jay Garrick" as the man behind the mask of Zoom, Caitlin did not allow her feelings to cloud her judgment on Zoom's misdeeds, rightfully recognizing him as "nothing but a monster" and refusing to accept Hunter's lingering affection for her. Nevertheless, Caitlin called upon those feelings, her face in tears, when she tried to influence Hunter to show his merciful side, sparing Barry Allen from certain death.
After her imprisonment with Hunter, it seems that Caitlin is suffering from post traumatic stress disorder(PTSD), due to her former lover and his frightening behavior and repeated displays of violence in front of her, seeing visions of Zoom when he's not there, and questioning if she still has her sanity.
Since Caitlin has been developing cryogenesis/cryokinesis abilities like her Earth-2 counterpart she has been terrified of becoming just like her. While reluctant to tell her friends she has used these powers to aid them occasionally without them knowing, but has gradually realized her inability to control them. This has made Caitlin very terrified but as a result of her changing biology she has become increasingly temperamental, which causes her appearance to become more like her Earth-2 counterpart. However, Caitlin is still sane enough to realize this but is only more horrified at her increasingly inability to manage her emotions. However, her desire to retain her humanity and her biology changing to make her more "cold", seems to be causing Caitlin to develop dissociative identity disorder.
Worrying about her new-found, uncontrolled powers, Caitlin's emotions become heightened enough that she became a vindictive, angry and cruel individual, similar, but not identical to Frankie Kane's split personality disorder. Also like Frankie, when affected by her powers, her eyes glow pale blue (while Frankie's glow pink). However, while Magenta tried to get rid of the Frankie persona altogether, Killer Frost state amplifies Caitlin's own fears, insecurities and bitterness. As Killer Frost, she mocked Barry by mentioning his most horrible failures including the deaths of his mother, father, Eddie and Ronnie, as well as revealing to Cisco that his brother, Dante was alive in the pre-Flashpoint timeline, before Barry changed it. She expressed bitterness over Barry only caring about himself and his own happy ending, while she was left broken.
Caitlin also mocked Cisco by calling him pathetic for feeling sorry that he had to hurt her to save Barry. She openly blamed Barry for what's happened to her, yet admitted that she feels broken. She nearly killed Julian and one of Alchemy's Acolytes, however she was still unable to kill Barry, making her snap out of her anger, as she became horrified at what she almost did.
Once Killer Frost was fully awakened due to Caitlin's temporary death and revival, she states that she doesn't want to be cured and wants Caitlin never to come back. She allies herself with Savitar after he reveals himself to her.
Killer Frost went after Tracy Brand after Savitar promised that if she lives up to her name and murders Tracy, she could be a god. She arrived at CCU in her new outfit and attacked Barry and Cisco, but when Barry fought back with fire, she ran away. She then attacked Tracy for the second time outside Jitters and continuously formed an ice slide that she slid on for a while without any difficulty. She took advantage of the fact that Cisco would not hurt her and almost hit him with a blast that Barry took. She stabbed Barry in the leg so that he couldn't follow her and she left, claiming that this is her now.
Later, Killer Frost kidnapped Joe's girlfriend Cecille outside of Joe's home and threatened to kill her if Joe and the team did not hand over Tracy to her and Savitar. Later at the supposed exchange site, she claimed that killing Cecille would bring her no joy but Tracy's death at her hands would. When Barry tried to talk her out of it, she knew exactly what Barry was going to say. She and Cisco later faced off, and while she seemed calm at first, she later fought back as hard as she can and lost to him. Cisco managed to get a sample of her blood, which could be the key to making a cure for her. Before Cisco can take her, Savitar arrived and took her away.
Despite all this, while reluctantly working alongside her former allies, it was shown she still has a strong attachment to her memories of working at S.T.A.R. Labs when she and Cisco reminisced about Ronnie losing his temper back when they were trying to build the particle accelerator. However. Killer Frost also showed in this moment that thinking about who she used to be made her uncomfortable as she quickly, sullenly, stated that she didn't want to stay any longer than she had to. Her conflicted feelings about herself and her old allies was again emphasized when she told Team Flash she never loved them and left, only for the assertion to hurt her heart enough to cause the real Caitlin to emerge for a few seconds once she was out of the team's sight.
Despite her continued allegiance to Savitar, Caitlin began showing signs of regret and doubt in her betrayal. During the final confrontation of Team Flash and Savitar, Cisco's unceasing loyalty for Caitlin finally enabled Caitlin's true-self to become permanently restored and reconciled with her friends. At the same time, she felt lost, unsure of who she is now.
Six months after restored to Caitlin, Killer Frost became stronger and eventually was able to regain control in various occasions. Recently Killer Frost's personality became similar to Caitlin's. After Iris conviced Killer Frost and Cailtin that they could co-exist they decided be allies and not enemies. Despite them now being allies, Killer Frost severely dislikes the color pink, well Caitlin does not.
In the future in which Iris dies, by the time of the year 2024, Caitlin has become too far gone to the point where she refuses to be called real name, as she prefers being called by her alias "Killer Frost", she becomes angry when people call her by her real name, despite her insanity and cold nature, Caitlin is very observant, she was able to realize that the Barry Allen she was speaking to was the younger-self of her Barry; due to the look on his face, as the latter had not yet become emotionally broken, as his Iris was not dead yet. This future was later erased when Savitar killed H.R. instead of Iris.
Powers and abilities
- "My name is Killer Frost."
- "Your name is Caitlin Snow."
"Can Caitlin Snow do this?"
- —Cisco Ramon and Killer Frost[src]
- Meta-human physiology: Prior to the Flashpoint event, Caitlin displayed no meta-human potential after being subjected to tests by several different sources. After the events of Flashpoint her powers developed, however, it is implied that her meta-human gene could have simply been dormant before.
- Transformation: After Caitlin and Killer Frost decided to be just one, Caitlin became able to transform into Killer Frost and vice-versa.
- Energy absorption/Cryogenesis/Cryokinesis: Caitlin's powers work by absorbing all existing heat around her, thereby reducing the temperature and to freeze targets well-below negative 370 degrees, even shattering beings as powerful as the Black Flash. Even more, her powers can reach such low levels that they can completely negate a speedster's healing powers and alternatively neutralize accelerated decomposing. Caitlin can create various ice structures with ease, even creating large bullet proof shields that can with standing point blank automatic rifle rounds, as well as launching upon manifestation sharp projectiles in rapid succession, creating an icy blade around her arm or as means of transportation, by producing icy waves of such propulsive strength, with one hand behind her, to propel herself forth across an ice slide she forms before her with her other hand, similar to Firestorm's fire-based propulsion ability. Her powers can also affect the weather around her, dropping the climate of the area and cause it to snow. She can also freeze objects without direct contact shown when she froze H.R's coffee from afar. A tell-tale sign of her accessing her powers is producing icy mist from her hands.
- Accelerated healing factor: While accessing her powers, Caitlin's metabolic rate is augmented to offset cold tissue destruction, allowing her endure more grievous injuries and likewise heal much faster than even a speedster, though foreign matter must first be taken out to not impede the healing. After clinically dying from a combination of a seizure and her reopened impalement wound, she was immediately resuscitated into a stable and cognitive state while her wound seamlessly healed completely in seconds. However, her healing powers only work when her Killer Frost side takes over, as wounds inflicted by Amunet left bruising and required stitches.
- Cold immunity: An added benefit to her powers, Caitlin also exhibits a high resistance to frigid temperatures. She is shown to be able to hold the ice constructs she manifests with little trouble. She was also seen unaffected after she escaped S.T.A.R. Labs, when there was a snowstorm.
- Freezing breath: Caitlin is able to create a fog with her breath. Around six months following the defeat of Savitar, Caitlin, as Killer Frost, grew powerful enough to orally produce cold mists with enough momentum to knock back several people off their feet.
- Transformation: After Caitlin and Killer Frost decided to be just one, Caitlin became able to transform into Killer Frost and vice-versa.
- Computer specialist: As a member of S.T.A.R. Labs, Caitlin is shown to have some technological skills of note, albeit not her main area of expertise as was evident in her ability to reprogram S.T.A.R. Labs satellite to track meteorological abnormalities over Central City, so they could find the location of Clyde Mardon.
- Expert medic: Caitlin is shown to be an expert in medical care, as seen when she was able to cure Barry Allen after he was poisoned by Kyle Nimbus, and later, when she was able to patch-up the former when he was seriously injured by Tony Woodward, Caitlin was also able to patch-up "Harrison Wells" after he was brutally beaten up by his Reverse-Flash speed mirage.
- Genius-level intellect: Caitlin is very intelligent, having a PhD and two doctorates. Her talents have been a crucial aid in helping Team Flash. Also, she, along with Cisco Ramon, were able to create a cure for Mirakuru.
- High pain tolerance: Caitlin is shown to have a remarkable level of endurance. Despite the grievous injuries she gained from Abra Kadabra, she was able to maintain consciousness through the surgery to remove the shrapnel in her body, all while instructing Julian.
- Trained neurosurgeon: Caitlin once mentioned that she knows how to perform a lobotomy, a procedure that requires both training and skill in the field of neurosurgery.
- Hand-to-hand combatant: To a yet to be elaborated degree during the past six months since Barry disappeared into the Speed Force, Caitlin as Killer Frost, demonstrated a measure of sheer hand-to-hand combat when she reversed an arm bar exerted upon her and then slamming the guilty party responsible, pinning him painfully against a pinball machine. It was later revealed that she worked as an enforcer for Amunet Black's illicit activities during periods when Killer Frost was active, explaining Caitlin's newfound fighting skills whenever her other side takes over.
- Marksmanship: Armed with a Cold Gun, Caitlin displayed being able to incapacitate a crazed Barry running wildly around S.T.A.R. Labs despite the fact that the latter was accelerated in super-speed and much faster than ever before. Even Cisco admitted he couldn't have hit Barry moving that fast with a vibrational blast.
- Carbine: Caitlin has implied that like her Earth Two counterpart, her powers have no effect on carbine.
- Power-dampening tech: If Caitlin is wearing power-dampening cuffs, she can't use her powers.
- Julian Albert's serum: Julian worked with Caitlin's mother, Carla Tannhauser to create a serum capable of removing Caitlin's powers. According to Caitlin, while the serum initially seemed to work, Killer Frost reemerged sometime afterwards, stronger than before, and was no longer affected by the serum.
- Borderline split personality disorder: Caitlin's changing biology also caused physiological effects. The more she would use her powers, the crueler and more sadistic she would become, showing no emotional attachment or regard for human life. While struggling to contain her powers, she developed a form of dissociative identity disorder which is triggered when angered, making it difficult to calm her down and restore her rationality. The change can be seen as the case of Caitlin's super-ego weakening in her psychic apparatus, allowing for her hidden fears, grudges and insecurities to come to the surface, rather than a true split personality. Over time, her friends continued trust and love for her finally let her overcome her mental damages, regaining her sanity while having full control over her power. However, six months later, having taken Julian's serum to cure her, it proved only temporary and had an additional side-effect of developing a complete separate personality. In addition to the changes happening more suddenly and erratically both ways, it also caused both the Caitlin and Killer Frost side to no longer have any recollection of the other's actions. After some words of inspiring encouragement from Iris, Caitlin and Killer Frost decided to be just the same person, Caitlin had no longer a problem with her Killer Frost side.
- Unstable control of powers: According to her mother, the continuous use of Caitlin's powers would end up making her unable to "turn them off", leading to Caitlin accidentally freezing her laptop. Caitlin seemingly began to use her powers (in small doses) with no adverse effect, as shown at Christmas 2016 when she made it snow. A tell-tale sign of her powers overwhelming her are the physical changes she gradually gains from them, such as her hair turning white and lips turning blue. The most noticeable sign of her losing control is her eyes glowing a pale whitish-blue and her distorted voice. The physical changes become more prominent as she makes use of her abilities, though they will recede if she goes long enough without using them, such as her hair going from white back to its original chestnut brown. However, as Killer Frost she is in full control of her powers, to the point where she was able to create a slide of ice to ride across the city. Caitlin is now able to control them through her Killer Frost side, who has now became her ally.
- Killer Frost suit: Caitlin wears a protective suit as her alter-ego, Killer Frost. After gaining full control over her powers and aiding her friends in the final battle against Savitar, she stops wearing it. However, after her Killer Frost side returns, Caitlin starts wearing it again when she is in battle.
- Power-dampening cuffs: After her powers began manifesting, due to her unstable control over them, Caitlin initially wore a pair of Cisco's power-dampening cuffs on her wrists as a means to help keep her powers in check. However, she abandoned use of these when she couldn't keep them charged for long periods of time and would have to sit with them plugged in, which she said made her "feel like a human tablet".
- Solar power collection pendant: Julian made Caitlin a pendant designed to dampen her powers, as well as to collect solar energy in order to help charge it whenever she went outside, so that it continues to work without constant recharging. However, upon her temporary death, Julian removed it. As Killer Frost, she destroyed it.
DC's Legends of Tomorrow
Freedom Fighters: The Ray
The Flash: Season Zero
- Interestingly, many villains in the series have expressed a degree of fondness towards Caitlin.
- Eobard Thawne often expressed his admiration for her abilities.
- Hunter Zolomon was in love with her and she was with him until learning of his true nature.
- Grodd has expressed genuine gratitude towards her and is one of the few humans including Eobard who he hasn't tried to harm.
- Savitar has considered Caitlin like a child of his.
- Hannibal Bates while disguised as Barry displayed an attraction to her, notably when he was staring at her butt and then kissed her.
- According to Caitlin herself, she practiced the Hippocratic Oath repeatedly as a child.
- In an erased timeline Caitlin is the first person to discover that Dr. Wells isn't paralyzed after she discovers his wheelchair vacant while they are at CC Jitters. However, due to Barry changing the timeline Caitlin remains unaware of this discovery, though she did learn the truth eventually along with everyone else.
- In a second erased timeline Caitlin, along with everyone in Central City, was killed by Vandal Savage using the Staff of Horus in his efforts to kill Carter Hall and Kendra Saunders. However, due to Barry Allen changing the time continuum this disaster never occurs.
- Although Killer Frost is a meta-human on Earth Two, Caitlin has explicitly stated that she has carried out tests which confirm that she does not have the meta-human gene, the first hint at a more subtle difference between the two worlds rather than the more explicit differences of certain characters having made different choices.
- It should be noted that Cisco, who was presumably tested after the accelerator explosion, wasn't aware he was a meta-human for almost two years, until his death in an erased timeline triggered his powers. It is possible that Caitlin could have been a meta-human ever since the particle accelerator exploded, with the same powers as Earth-2 Caitlin, but hadn't triggered the gene for nearly four years.
- It is likely that the reversal of Flashpoint is what caused her abilities to activate, as Earth Two Harrison Wells used his metahuman detector on her and it did not go off, even though Cisco, whose powers were only just beginning to appear, then immediately set it off.
- The major difference between the two is that Caitlin is kind and compassionate, fearing losing that side of herself; Killer Frost from Earth Two is cruel and sadistic.
- It should be noted that Cisco, who was presumably tested after the accelerator explosion, wasn't aware he was a meta-human for almost two years, until his death in an erased timeline triggered his powers. It is possible that Caitlin could have been a meta-human ever since the particle accelerator exploded, with the same powers as Earth-2 Caitlin, but hadn't triggered the gene for nearly four years.
- After both her original persona and Killer Frost persona merge, Caitlin's appearance changes slightly from her former villain appearance. Her skin is no longer pale white, with her lips returning to a normal rosy color. He pale white hair also has taken on a blonde-like color.
- Apparently Caitlin Snow doesn't exist on Supergirl's Earth. However as shown by Jay Garrick being Henry Allen from Earth Three, same versions of people do not necessarily have the same name.
- While Caitlin was revealed to have powers in the end of "Paradox", some of the struggles she's been going through are similar to Siobhan Smythe/Silver Banshee when it comes to being scared having powers, the stress they had and have to go through before and after they manifest, and the trauma brought upon them by friends like Cisco and Winn not being trusted on keeping the most personal secrets from others over what the know is right and wrong.
- The only difference between the two friends of the hackers turning to the darkside is that Siobhan was able to maintain her mental stability by maintaining further sense of optimism while Caitlin can not because she fears becoming her doppelganger and because of the hassle Zoom caused Barry on his last rebound with his archenemy from Earth Two that she didn't want to make problems worse for him.
- Though not admitting it, some of Caitlin's actions have made it clear that she is attracted to Barry.
- While at the dive bar with Barry where the two look for new love interests, she gets drunk and drops several hints of her attraction to him, even singing "Summer Lovin" with him and flirtatiously joking about it when she realizes afterwards that he's actually a very good singer. She later, while still drunk, asks him to help her change out out of her clothes to her night garb and then asks him to tuck her in.
- When Hannibal Bates disguises himself as Barry and kisses her to distract her from working on serum to use against Hannibal, she is surprised initially and stops him but when he kisses her again, she passionately begins to make out with "Barry" until Iris arrives, causing the two to awkwardly pretend it never happened. When Hannibal disguises himself as Caitlin while trapped in the pipeline to attempt to flirt his way out by calling Barry "handsome" he smirks and looks over to Caitlin only for her to awkwardly fakeingly deny that she would say that.
- When Caitlin turned in Killer Frost the first time, no one could return her normality, but when she almost killed Barry she was horrified for this action and turned back in Caitlin for own will.
- When Caitlin turned in Killer Frost the second time she allied with Savitar only when he showed his true face: A future and evil version of Barry Allen.
- After Ronnie's death, Caitlin was in two relationships, first with Hunter Zolomon and then with Julian Albert, the first when she believed that he was a good person and a hero in his earth, and Julian who is a crime scene investigator for the Central City Police Department. Barry, Hunter and Julian all balance between two types of people; a civilian and a hero.
- In "", Cisco states that Caitlin has two doctorates and a PhD.
- Caitlin's measurements are 34-25-34.
- As clearly shown in the show, Caitlin is not that close to Barry, but is with the rest of the team.
Behind the scenes
- In the DC comics, Caitlin Snow is known as the third iteration of the super-villain Killer Frost. In the first season finale there is a brief glimpse of Caitlin as Killer Frost when Barry travels through time.
- Caitlin says in "" that Ronnie referred to them as a couple as "fire and ice", a reference to their respective DC comic identities.
- Furthermore, Caitlin is often seen wearing blue, another possible reference to her super-villain alter-ego in the DC comics.
- In the DC comics, unlike other incarnations of Killer Frost, Caitlin is a protagonist/anti-hero rather than a super-villain. However, in the Arrowverse, Caitlin's Earth-2 counterpart fulfills the traditional Killer Frost role.
- In season 3's "", executive producer Todd Helbing dubs Caitlin's metamorphosis as "Caitlin Frost" demonstrating that it was one of the slow progressive steps in her fulfilling her eventual destiny.