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"I already left once before. Left both of you. Worst mistake I've ever made in my entire life. I wasn't going to make that again. Family shouldn't leave family."
—Thomas's last words to his wife and daughter[src]

Dr. Thomas Snow (died April 23, 2019) was the husband of Carla Tannhauser and the father of Caitlin Snow and the creator of the late Frost. He was believed to have died in 1999 from ALS. 19 years later, however, it was discovered by Ralph Dibny that Thomas' death certificate was a fake. Throughout the years he developed a split personality, later nicknamed Icicle by Cisco Ramon and Nora West-Allen,[1] as a result of his meta-human ALS disease treatment. He was killed after sacrificing himself to save his daughter from Cicada.[2]


Early life[]

The Snow family

The Snow family.

Thomas Snow was a geneticist. At some point, he married fellow scientist Carla Tannhauser and in February 1989,[3][4] they had a daughter, Caitlin Snow.

Thomas was very close to his daughter and they would watch old holiday movies together at Christmas on snowy nights.[5] He furthered Caitlin's interest in science and the two partook in many educational activities and games together, including looking at the constellations through their homemade telescope and studying bugs from the backyard. While teaching Caitlin the periodic table, Thomas and his daughter often played a game in which they created their own set of elements.[4]

Icicle and Killer Frost[]

Around 1999, Thomas began suffering from amyotrophic lateral sclerosis (ALS).[6] To prevent it from spreading, Thomas experimented on himself using cryogenetic therapy and eventually managed to freeze the progression of the disease. In the process, however, Thomas ended up creating Icicle, a malignant alter-ego. After this incident, Thomas realized that Caitlin had inherited his gene for ALS and used experimental cryogenic therapy to save her as well. While the experimental trials successfully cured Caitlin of the disease, they also left her with a dormant cryokinetic-powered alternate personality, whom Thomas called "Khione" after the Greek goddess of snow.[1]

At some point when Caitlin was a child, Thomas took her out for a ride on her bicycle. However, Caitlin fell off her bike in front of an approaching car and Thomas rushed to her aid. Upon seeing his daughter's transformation into Killer Frost, he tried to prevent Caitlin from seeing her reflection.[7]


As his ALS apparently worsened, Thomas tried to hide his symptoms from his family, not wanting them to worry. Carla tried to cure her husband as he fought the disease for years. However, he eventually passed away from the ailment, much to Caitlin and Carla's heartache.[6][7]

After Thomas' supposed "death", Carla buried herself in her work in an attempt to cope with the pain, neglecting Caitlin in the process. As a result, Caitlin and Carla became estranged from one another for years.[8]

After going underground, Thomas kept in touch with several scientists including Louise Lincoln, Victor Fries and Harrison Wells.[1]


In May 2018, Ralph Dibny discovered that Cameron Mahkent, the judge who signed Thomas's death certificate, didn't exist, casting doubts on the credibility of his death.[9] Cisco used his vision powers on Caitlin and the death certificate to discover who forged it, and Caitlin saw her mother signing it.[10]

After some investigating, Caitlin uncovered several mysterious documents detailing her father's work in non-existent elements and an apparent suicide note from her mother's company file room. However, after analyzing the molecular structures of the elements and comparing them with her childhood periodic table, Caitlin deciphered a message from her father which read "CAITLIN COME FIND ME".[4]

Revealing his true self[]

Caitlin, Barry Allen and Cisco Ramon eventually tracked Thomas down to an abandoned black-ops facility owned by Tannhauser Industries.[11]

However, it was later discovered that he was also a cryogenic meta-human that had an evil split personality that attacked the team. The personality wanted to use a serum, that Caitlin reluctantly created, to kill off Thomas for good and inhabit the body himself. Just as he was about to inject himself, Caitlin managed to break through the mental block that DeVoe had created, allowing Killer Frost to emerge and shoot him back with an ice blast. He quickly attempted to convince Frost to take the serum as well and work with him but she refused, stating that Team Flash was her true family. As she walked towards him, she stood on and destroyed the serum. She created an ice-fist and began to punch him but stopped as Thomas' personality emerged and spoke to Caitlin. This turned out to be a short reunion as the evil personality reemerged and knocked her back with an ice blast, proceeding to use two ice blasts to launch himself into the air and escaped.[1]


Caitlin fights Thomas

Icicle battling Frost.

Icicle later returns intending to eliminate Caitlin and Carla's human sides. Just as Icicle is about to kill Caitlin, Thomas suddenly finds the strength to return to his human form. Then, Cicada appeared and knocked out Barry, so, Caitlin dismissed Thomas and Carla. They then went fighting, where Caitlin fell to the ground. As she recovered, Cicada threw the dagger at Caitlin, but Thomas jumped into the daggers path, sacrificing himself for Caitlin, and died in her arms.[2]


Original multiverse[]

Thomas's death was avenged when Team Flash erased Future Grace from existence by destroying the dagger and curing her younger-self.[12] Furthermore, his death helped Barry Allen and his daughter, Nora West-Allen, to reconcile with his last dying words to his family "family should never leave family".

New multiverse[]

When Carla sees Frost, she thinks of the ordeal caused by Icicle.[13]


Thomas was a very loving, supportive husband and father. He encouraged Caitlin's interest in science and always pushed her to be the best she could be. Thomas was known to be a simple, playful, and fun-loving man, contrasting his wife Carla Tannhauser's more stern nature.

Powers and abilities[]


  • Meta-human/Cryogenic physiology: After suffering from multiple sclerosis, Thomas began to use experimental cryogenic therapy to save himself, as he did to Caitlin sometime later. Due to this, he gained cryogenic-based powers and also developed a dual-personality (i.e. Icicle).[1]
    • Transformation: Similar to Caitlin and Killer Frost, Thomas is able to transform into Icicle and vice-versa. However, unlike the former, the Icicle personality retains most of the control over his body.[1]
      • Thermokinetic cryokinesis: Given the fact he used similar treatments on his daughter, it is likely that Icicle's powers work in a similar fashion to Frost's. He can thus create sheets of ice, or shoot spearlike icicles at opponents. Icicle can also create an ice slide and use his cryogenic powers to rapidly propel himself forward on the slide.[1]
        • Cryokinetic breath: Icicle can exhale cold mists to create mini ice crystals in his victim's lungs, which makes it difficult for them to breathe.[1]
        • Cold immunity: As a byproduct from his cryogenic powers, Icicle's cells can withstand subzero temperatures, as seen when he used a machine to lower the temperature of a room to absolute zero.[1]
        • Flight: By generating cryogenic thrusts towards the ground, Icicle can continuously propel himself into the air, creating a simulated version of flight.[2]


  • Genius-level intellect/Master geneticist: Thomas was an extremely intelligent scientist and an excellent geneticist.[1]



The Flash[]

Season 2

Season 3

Season 4

Season 5

Season 6

Season 8

Season 9

The Chronicles of Cisco[]


  • Thomas loves peanut butter and jelly waffles for breakfast.[1]

Behind the scenes[]

Caitlin Snow's father

Thomas Snow as seen in "Monster".

  • Icicle is a legacy name used by three different characters in the DC comics, two of which villains, father and son. Thomas Snow seems to be based on the latter, Cameron Mahkent, as his name is the one the former used to fake his own death by making up a judge who doesn't exist.