Formerly known as Dr. Harleen Quinzel, a promising psychologist and intern at Arkham Asylum, Harleen became obsessed with her asylum subject, the Joker. After falling in love with him, she helped the Joker escape Arkham.
Harleen’s relationship with the Joker led her to adopt a new sidekick/love interest identity – Harley Quinn – whether the Joker wanted one or not.
Harley eventually came to think that the Joker was holding her back and struck out on her own. She became a member of several vigilante/justice groups, including the Suicide Squad, the Gotham City Sirens and a travelling sideshow.