Caitlin Snow


 * For her Earth Two equivalent, see Caitlin Snow (Earth Two).

"Snow, you're a tremendous scientist, but an even better person"

- Harry Wells to Caitlin Snow

Dr. Caitlin "Cait" Snow is a former scientist at Mercury Labs and a bio-engineer at S.T.A.R. 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 his true identity as Eobard Thawne, and provides medical support for the team. Caitlin is also the widow of the late Ronnie Raymond, and is close friends with Cisco, Barry and Felicity Smoak.

Early life
Caitlin's father suffered from multiple sclerosis and despite fighting it for years he eventually died, much to Caitlin's heartache. Caitlin has an estranged relationship with her mother for reasons even she never understood. Based on what her Earth-2 counterpart would later tell her version of their family, it's implied that Caitlin has/had a brother named Charlie she is isn't aware of.

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 in to 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 super fast, 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 he tripped over in to barrels of water. 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 suit Barry's purposes well. 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 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 in to 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 in to 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 in to 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 was 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 to threaten Snart.

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, every one 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 debate 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 among multiple injuries in his whole body. She later watched as Barry practiced fighting on a robotic dummy and dislocated his arm 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 arm by brutally snapping it back in place with her hands. Caitlin and Cisco later deduced Tony's hiding place 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 ran over 800 miles but Caitlin begged him not to as it would shatter every bone in his body if done wrong. Later Barry engaged Tony again after he kidnapped Iris and both Caitlin begged him to leave which he did, only he turned around to run at 800 miles which Caitlin begged him not to 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 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. Despite succeeding however the wormhole reopened, as a result of a paradox from Eddie killing himself to erase Eobard from existence, and the team were helpless to watch it grow and begin consuming everything in Central City before it would eventually consume the world. Flash however sped off into the portal itself to close it and stabilized it's range but wasn't able to close it. Professor Stein informed Ronnie the only way to destroy it would be to separate inside it but Caitlin immediately protested by 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 and encountering Zoom
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 quickly denied when Iris implied it. 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 on Earth, 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 tells Caitlin that his cells were mutated after becoming The Flash, and Hunter's cells are 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 it's 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 it's 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 metahuman named "Killer Frost" who was a serial killer, and Cisco expressed worry because Caitlin is acting just like Killer Frost. However Caitlin stated that if she lets 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 Jay 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-1 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-2.

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-1. 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-2 revealed her mother was a frigid narcissist because her brother Charlie died, though Caitlin-1 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-1 and took him with her so she could watch.

Personality
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 polar-opposites, 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 acute stress reaction, much like her lover due to 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.

Abilities

 * Genius-level intellect: Caitlin is very intelligent, as evidenced by the crucial role she plays in Team Flash, she along with Cisco Ramon were able to create a cure for Mirakuru.
 * Computer specialist: As an 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 Eobard Thawne after he was brutally beaten up by his Reverse-Flash speed mirage.
 * 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.

The Flash
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 * {{Ep|Pilot|page=Pilot (The Flash)}}
 * {{Ep|Fastest Man Alive}}
 * {{Ep|Things You Can't Outrun}}
 * {{Ep|Going Rogue}}
 * {{Ep|Plastique}}
 * {{Ep|The Flash Is Born}}
 * {{Ep|Power Outage}}
 * {{Ep|Flash vs. Arrow}}
 * {{Ep|The Man in the Yellow Suit}}
 * {{Ep|Revenge of the Rogues}}
 * {{Ep|The Sound and the Fury}}
 * {{Ep|Crazy for You}}
 * {{Ep|The Nuclear Man}}
 * {{Ep|Fallout}}
 * {{Ep|Out of Time|page=Out of Time (The Flash)}}
 * {{Ep|Rogue Time}}
 * {{Ep|Tricksters}}
 * {{Ep|All Star Team Up}}
 * {{Ep|Who is Harrison Wells?}}
 * {{Ep|The Trap}}
 * {{Ep|Grodd Lives}}
 * {{Ep|Rogue Air}}
 * {{Ep|Fast Enough}}

Season 2

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The Flash: Season Zero

 * "The Strongman Cometh"
 * "Who Let the Chimps Out?"
 * "A Goodnight Hiss"
 * "Big Top Brawl"
 * "A Captive Audience"
 * "Showtime"
 * "The Big Finale"

Trivia

 * 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 in 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 metahuman for almost two years, until his death in an erased timeline triggered this powers. It is possible that Caitlin could in fact be a metahuman with the same powers as Earth-2 Caitlin, but has yet to trigger the gene.
 * 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.
 * Caitlin noted that she has never had a brother when her counterpart mentioned him while they both were Zoom's captives. However that's left ambiguous since the multiverse has doppelgängers in every earth that lead parallel lives to each other leading to the conclusion Caitlin might have had repressed her memory of him if he was alive by the time of her childhood.

Behind the scenes

 * Caitlin Snow is better known from the DC comics as the fourth iteration of the super-villain known as 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.
 * Unlike other incarnations of Killer Frost from the DC comics, Caitlin is a protagonist rather than a super-villain. However Caitlin's Earth-2 counterpart fulfills the traditional Killer Frost role. However, in "Fast Enough", the Speed Force shows her as Killer Frost in the future, leading to an assumption that she will take on this role.