Doctor Harleen Frances Quinzel is a former psychiatrist, previously employed at Arkham Asylum, a former criminal, a mercenary, and the ex-girlfriend of the Joker, operating under the alias Harley Quinn. After being manipulated by the Joker into assisting his escape from Arkham, Harleen was submerged in a batch of chemicals at Ace Chemicals, re-emerging as the Joker's right-hand woman. Over the years, Harley has become a nemesis of the Batman, growing to become known as the queen of Gotham City alongside the Joker, notably committing numerous crimes, and while her allegiance with the Joker meant she was never in any real danger, her long history of violence would later catch up with her.