Leonard Snart was a professional thief operating in Central City. His father was a (bent) cop, and he had learned from a young age to study the police to make sure he got away before they could respond. Leonard grew up resenting his father for the abuse he put him and his sister through.
Before the S.T.A.R. Labs particle accelerator explosion that released a wave of superpower-creating dark matter throughout Central City, Leonard Snart was a successful bank robber and thief. He operated for a time with Mick Rory before the two parted ways on good terms. Later, he would go on to work with Sam Scudder and Rosa Dillon, two thieves that did not share his desire for professionalism.
On the night of the explosion, Snart went to confront Scudder and Dillon at their hide out for using their cut of the last heist too quickly, allowing for a greater chance to be caught by the cops. Scudder and Dillon did not like Snart's tight rules so they quit the team. Snart responded by fighting the two and preparing to execute Scudder with his handgun but was chased off when he saw the explosion in the sky. By leaving the two criminals beaten up in the hide out, the dark matter affected them, giving them superpowers, and trapping Scudder in the Mirror World for three years. 
Snart decided to go after the Khandaq Diamond, which came to the city for an exhibit at the Central City Museum. He planned the heist to occur during transit, because it allowed him twice as much time before the police would arrive. He had not counted on the Streak, who got there much quicker. In the ensuing fight, Snart got away, but his foe left him dumbfounded. He studied the footage from the heist and discovered it was a fast-running man. He needed to up his game if he were to beat this foe.
Becoming Captain Cold
Leonard obtained a specialized gun that shot out a focused beam of cold, which was stolen from S.T.A.R. Labs. He used it to rob the museum, and in his confrontation with the speedster he found his weakness: the need to save people. This allowed him the time to escape and plan his next move.
In order to lure out the streak, Snart feigned an escape on a busy train, out in the open. The trap was sprung. Leonard froze the wheels of the train using the gun, which meant the streak was too busy saving people to go after him. Tired from unloading the packed train, the speedster proved an easy target. However, before he could finish him, a team from S.T.A.R. lead by Cisco Ramon intervened, and threatened to unleash a bigger cold gun on him. He backed away, but escaped with the diamond.
Some time later, in a Keystone City motel, Leonard met with an old accomplice of his, Mick Rory. Because the face of justice in the city had changed, they needed a new approach to villainy. He knew his old pyromaniac friend could not refuse the offer once he gave him a special heat gun.
After the singularity event, Barry was approached by Lisa Snart. She had concerns that Leonard had been kidnapped. Lenny's position was tracked based on his Cold Gun pulling ultraviolet rays out of the air. When Barry approached Leonard, Barry was surprised to find Lenny was willingly working with his father on a robbery. Leonard then froze Flash with his Cold Gun and left with his father.
Later, Barry learned that Lisa had been implanted with a bomb and theorized that Leonard was being forced to work with his father to save his sister's life. He approached Leonard as an undercover bomb technician to assist them in their next heist. When Barry told Leonard that the bomb had been successfully removed form his sister, Leonard quickly turned on his father and froze him with his cold gun. He was then brought to Iron Heights where Barry told him he was a criminal with a code.
Joining the Legends
Soon, Snart and Mick Rory were contacted by Rip Hunter, a time traveling disgraced Time Master, who wanted their aid in hunting down the immortal tyrant Vandal Savage for killing his wife and child. Captain Cold and Heatwave were chosen because of their unimportance to their original timeline. He sacrificed his life to stop the Time Masters.
- Leadership: Snart was the leader of a successful band of robbers before getting his Cold Gun.
- Thievery: Snart is the greatest robber of Central City, being able to plan a heist several weeks in advance. Having no Metahuman skills, Snart relies solely on his wit and tech, pulling off numerous successful heists. He is also capable of stealing wallets from people when distracting them with conversation.
- Surveillance: Snart regularly listens in on police radio chatter. He successfully determines the response time of the cops for his heists. However, his numbers were thrown off by the response time of the speedster.
- Hand-to-Hand Combat (Advanced): Having suffered abuse from his father and in juvie, Snart learned how to defend himself. Because of the years he spent as a thief, he is well-trained; he is on even fighting terms with Mick. He is capable of holding his own against at least one properly trained soldier.
- Marksmanship: When armed with a normal gun, Snart has shown a great deal of skill. He is able to kill a Wild West outlaw before he had a chance to shoot Professor Stein, with barely a movement. He is also a great sniper, being able to knock guns out of enemies' hands with single shots.
- Sister: Leonard deeply cares about his little sister, as he pretty much was the one who raised her while their father was in and out of prison. Because of such, he is protective of her.
- Kleptomania: Snart steals things on impulse.
- Captain Cold's Cold Gun: After Barry Allen was struck by lightning and taken to S.T.A.R. Labs, Cisco Ramon began secretly developing a special weapon that could be used to counteract Allen's super speed, in case the speedster had any malevolent intentions when he woke up from his coma. The gun had the ability to slow molecules down in objects, therefore making them extremely cold. Due to the lack of security at S.T.A.R. Labs, though, the device was stolen by a thief disguised as a janitor. The thief then attempted to sell the weapon to Leonard Snart, who instead stole the weapon himself to use against the new hero.
- This version of the character is exclusive to the continuity of the television series The Flash and is an adaptation of Captain Cold. The original character was created by John Broome and Carmine Infantino and first appeared in Showcase #8.
- Captain Cold is played by Wentworth Miller.
- 36 Appearances of Leonard Snart (Arrow)
- 5 Images featuring Leonard Snart (Arrow)
- 8 Quotations by or about Leonard Snart (Arrow)
- Character Gallery: Leonard Snart (Arrow)
Legion of Doom member