Dr. Harleen Frances Quinzel, aka Harley Quinn, first appeared in Batman: The Animated Series in the 1992 episode "Joker's Favor". She was introduced as Joker's love interest and partner in crime.

Harley Quinn wearing her villain outfit, in front of an audience with a microphone in her hand.
Image/Warner Bros. Pictures

In 1994, the graphic novel The Batman Adventures: Mad Love told Harley Quinn's origin story. Written and drawn by Dini and Timm, it shows us Dr. Harleen Frances Quinzel, Ph.D. as an Arkham Asylum psychiatrist. Joker is her patient, and she is fascinated by him. During their sessions, she falls in love with him, eventually helping him escape from the Asylum multiple times. The last time, she wears a jester costume and becomes Joker's sidekick.

Later, in the 2019 animated series, Harley Quinn becomes fed up with Joker's domineering ways and manipulations and leaves him to be "an independent woman". She meets up with Poison Ivy, they set up house together, and go on a crime spree.

Although she was introduced as Joker's love interest in the animated series, she clearly developed a romantic relationship with Poison Ivy. Harley Quinn writers Jimmy Palmiotti and Amanda Conner confirmed that Harley and Poison Ivy are in a relationship.

The 2019 animated series openly portrays Harley's bisexuality, and has no problem showing the romance between Poison Ivy and Harley.

She was portrayed by Margot Robbie in the 2016 film Suicide Squad and the sequel in 2021. She was also the star of Birds of Prey in 2020.

In the upcoming 2024 movie Joker: Folie à Deux, she's portrayed by the bicon Lady Gaga.