Leonard Snart was raised by an abusive father and took refuge with his grandfather, who worked in an ice truck. When his grandfather died, Snart grew tired of his father's abuse and set out to start a criminal career. Snart joined up with a group of small-time thieves and in planning out a robbery, each was issued a gun and a visor to protect their eyes against the flashes of gunfire. This visor design would later be adapted by Snart into his trademark costume. In recent years he has added a radio receiver to them which picks up the police band to monitor local law enforcement. Snart and the other thugs were captured by the Flash and imprisoned. Snart decided to go solo, but knew he had to do something about the local hero, the Flash.^[3]

Snart read an article that theorized that the energy emissions of a cyclotron could interfere with the Flash's speed. He designed a weapon to harness that power and broke into a cyclotron lab, intending to use the device to charge up his experimental gun. As he was finishing his experiment, a security guard surprised Snart. Intending to use his gun only to scare the guard, he inadvertently pulled the trigger and discovered that his weapon had been altered in a way he had never imagined. The moisture in the air around the guard froze. Intrigued by this twist of fate, Snart donned a parka and the aforementioned visor and declared himself to be Captain Cold - the man who mastered absolute zero. Snart then committed a series of non-lethal crimes, on one occasion placing the city in suspended animation in an attempt to force Iris West to marry him as he had fallen in love with her when he saw her in the prison, but the Flash got through a wall of ice and was able to reverse the process. He later fell in love with a newscaster, and competed with Heat Wave (in his first appearance) over her in a crime spree, but they were both beaten by the Flash. But after Barry Allen's death, during the Crisis on Infinite Earths, Captain Cold became a bounty hunter with his sister Lisa, the Golden Glider.^[3]

During the events of Underworld Unleashed, Captain Cold lost his soul to Neron but Wally West brought it back to the land of the living. He soon returned to crime, this time a member of Wally's Rogues Gallery. The Rogues had first been assembled when another Flash foe, the super-intelligent Gorilla Grodd had broken them out of jail to distract the Flash. The Golden Glider had abandoned her bounty hunter career and had started partnering with a series of thugs who she dressed in a costume, armed with a copy of Captain Cold's signature Cold Gun, and called Chillblaine. Already distraught over the death of her lover, the Top, it seemed that the supposed death of her brother pushed her over the edge. But the last Chillblaine was a little smarter and more vicious. He murdered the Golden Glider, prompting Captain Cold to hunt him down, torture him and kill him by freezing his outer layer of skin and then pushing him off a high rise building. Not long after that, Snart was framed by a new incarnation of Mister Element. He used his Element Gun to simulate Cold's gun, using ice and cold to murder several police officers before Captain Cold and the Flash discovered who was actually responsible. With the death of his sister, and having killed Chillblaine and Mr. Element in vengeance, Cold has again become an unrepentant criminal. However, during a confrontation with Brother Grimm, Cold actually worked with Wally West to defeat the powerful magic user, although this was mainly because he and Mirror Master had been betrayed by Grimm and wanted revenge.^[3]

Captain Cold was declared the leader of the Flash's Rogues Gallery. His skill and experience have made him a strong leader to the likes of the Weather Wizard, the new Trickster, the new Mirror Master, and the new Captain Boomerang. Len seems to have taken the young Captain Boomerang under his wing, after the elder Boomerang was recently killed. Tabloids rumoured that Captain Cold's sister, the Golden Glider, was Boomerang's mother, making him Captain Cold's nephew. This turned out to be false, however, as the new Boomerang's mother has been revealed to be Meloni Thawne, who is also the mother of Bart Allen. Despite his more ruthless nature as of late, Captain Cold's heart is not completely frozen, evidenced by having sent flowers to honor Sue Dibny, murdered wife of the Elongated Man.^{[volume & issue needed]}

Traditionally, Captain Cold is driven by three things: money, women, and the desire to beat Barry Allen. Although not the lecher that Captain Boomerang was, Len Snart has an eye for the ladies, particularly models. When Barry Allen died, Captain Cold drifted for a while, jumping back and forth over the lines of crime and justice. He was captured by the Manhunter and served time in the Suicide Squad, worked with his sister as a bounty hunter (Golden Snowball Recoveries), and, with his longtime friend and sometimes nemesis Heat Wave, encountered Fire and Ice of the Justice League. He has teamed up with various villains over the years other than the many Rogues. These include Catwoman and the Secret Society of Super Villains. His favorite baseball team is the Houston Astros