Leonard "Leo" Snart is a rebel from Earth-X, serving as a member of the Freedom Fighters. He is the husband of Ray Terrill. After meeting the superheroes from Earth One, he decided to join the Legends, using his skills at psychotherapy to help them with the loss of Martin Stein, while grieving about his own loss of his Earth's Mick Rory.
At some point Leo became a member of the Freedom Fighters, a group openly opposed to the Nazi rule over Earth-X. He was a freedom fighter alongside his best friend, Mickey, growing up together in the resistance. When Mickey died, saving police officers from fire, Leo was devastated, a grief he kept with him up until meeting Mickey's counterpart from Earth One, Mick Rory.
Leo saved Ray Terrill, Oliver Queen, Barry Allen, Jefferson Jackson, Martin Stein, Sara Lance and Alex Danvers from being killed by a firing squad commanded by a Sturmbannführer. Leo and Ray helped the team reach a breach located in a Nazi base to return to Earth One where they participated in the defeat of the Nazis, Eobard Thawne, Oliver and Kara. In the end, Cisco Ramon breached Ray back to Earth-X, though Leo chose to stay behind on Earth One for a bit and later attended Stein's funeral where he held onto Mick Rory while Mick was crying, telling him to let his feelings out. Following the Crisis, he bid a temporary farewell to Ray Terrill and the Freedom Fighters, deciding to explore Earth One, joining the Legends. He had a short tenure with them and decided leave once he felt his adventure with them was over; he bid them farewell and told that once he was back home he would marry his Ray.
Team Flash later enlisted Leo Snart's help to safely transport Neil Borman into A.R.G.U.S. protective custody on Earth One. During this exploit, Leo revealed to Team Flash that he and Ray had gotten engaged. Later, Leo recognizes Barry being emotionally detached due to the death of his teammate, Ralph Dibny, and encouraged the Flash to embrace his grief. Afterwards, Cisco gave Leo an interdimensional extrapolator as a wedding gift, which the latter then used to return to his own universe.
- "Tease me all you want for being sentimental. These heroes would risk everything for the people they love, just like I would. For you."
- —Leo Snart to Ray Terrill[src]
Leo is shown to highly despise the Nazi rule over Earth-X. He is an optimist and a bit of a show-off, chastised for his risky "dramatic entrance" by Ray Terrill. Like his Earth One counterpart, he is extremely sarcastic, and also has a flirtatious streak, flirting with Sara Lance and Oliver Queen. Nevertheless, he can be serious at times, especially when the situation concerns his boyfriend, Ray Terrill, whom Leo loves dearly. Also unlike Earth One Leonard, who follows "four rules" when it comes to planning; "make the plan, execute the plan, expect the plan to go off the rails, throw away the plan", Leo prefers to carefully (even obsessively) plan his strategies, and stick with that plan regardless.
Leo has shown a peculiar aversion to chaotic fighting, claiming that Mick Rory "can't just go around roasting people" without due process, even though the two were in the middle of fighting Schutzstaffel troops. Leo is also quite adventurous, finding Earth One to be lovely and deciding to stay and explore this new universe. In all, Leo is different from his Earth One counterpart, having an optimistic and chipper attitude that even Earth One Leonard at his most heroic never truly possessed.
- Marksmanship: Leo is a proficient marksman, primarily using his Cold Gun.
- Psychotherapy: Leo was trained in psychotherapy and tried to use his skills to help the Legends, grieving over the death of Martin Stein, and especially Mick Rory, whom he found to be having alcoholism-related problems.
- Cold Gun: Leo Snart has a Cold Gun similar to that of his Earth One counterpart.
- Interdimensional extrapolator: Cisco gave Leo an Interdimensional extrapolator to allow the latter to freely travel between Earth-X and Earth One.
- Martin Stein puppet: Leo Snart had a puppet of Martin Stein to help the Legends grieving over Martin's death. He got rid of it when he discovered that it wasn't helping and due to Mick Rory being scared of puppets. 
DC's Legends of Tomorrow
The Chronicles of Cisco
- In the DC comics, Citizen Cold is the identity of Leonard Snart from the Flashpoint timeline. Much like the series, he was a hero who replaced the Flash as the hero of Central City. Unlike the series, the DC comics version of Citizen Cold was ruthlessly defensive, even killing Wally West sent by Iris West to investigate Citizen Cold's true identity.
- Citizen Cold uses the visor that Captain Cold and Citizen Cold wear in the DC comics, contrasting with his Earth One counterpart that wore a pair of blue goggles.
- Leo Snart is the first member of the Legends who doesn't originate from Earth One.
- Aside from his partner Ray Terrill, Leo also appears to have attractions towards Oliver Queen, Sara Lance and John Constantine.
- Leo identifies himself as gay, implying his attraction toward Sara was just friendly. Though gay, he does know a hot woman when he sees one.
- Leo kept count of how many allies he lost to the Reich. He grieved for each one before trying to move on, as he knew the guilt would interfere with any attempts to plan.
- Leo appears to have a low opinion of his Earth One counterpart's advice to Barry in "Infantino Street" as "terrible advice". He also didn't seem very fond to learn his Earth One counterpart was a thief and a murderer.