Harleen Quinzel was born in Canarsie, Brooklyn, New York, the oldest of four children and the only girl. Her interest in criminal psychology grew early in her childhood.

Best known as the former girlfriend of the Joker, Harley suffers from multiple personalities, homicidal tendencies, Stockholm syndrome and possibly "shared psychotic disorder."

Harley Quinn is a Caucasian young woman with bleached white skin and blue eyes. Harley has an athletic body type, coming from her past as an acrobat.