Caitlin Snow

Caitlin Snow was a moderately successful meteorologist living in Central City. However after being trapped in an experimental thermo-chamber she became Killer Frost and an enemy of The Flash.

Early Life
Caitlin Snow joined the team at S.T.A.R. Labs and began a relationship with her co-worker Derrick O'Connell. She begins working on a thermo-chamber - a chamber to create artificial environments (specifically cold) which can be used to test new technologies.

Becoming Killer Frost
One night Caitlin arranged a surprise for her partner, Derrick, in their lab and was going to find him when she heard him coming, and she hid to surprise him. However, he arrived with another woman, and Caitlin hid inside the thermo-chamber.

Unknowingly Derrick activated the chamber, exposing Caitlin to chemicals and turning her into a metahuman. Caitlin then tracked Derrick and exacted revenge for his betrayal by freezing him. She then decided that she was going to kill all unfaithful men, and set out on a new mission.

She came face to face with the Flash on one of these kills, and was able to trap him in ice before leaving.

Later she attacked the Hot Kiss strip joint, killing the doorman and several other clientele. She was captured by The Flash after giving her her nickname: Killer Frost.

Killer Frost then teamed up with Victor Creed to escape the CCPD, and the team set a trap for The Flash, failing due to the work of Lois Lane.

Killer Frost had a brief relationship with Victor, but decided to split and rob a museum. Frost tried to abandon when the Flash arrived, but was forced to face the speedster and her ex-partner before being arrested once more.

Trivia

 * Killer Frost was the first female villain of The Flash
 * Killer Frost was also the first villain of The Flash to truly defeat him.