Harley Quinn (Dr. Harleen Frances Quinzel) was first introduced as a villain on September 11, 1992, in the animated series Batman: The Animated Series, later adapted into DC Comics' Batman comic books. As suggested by her name (a play on the word "harlequin"), she is clad in the manner of a traditional harlequin jester. The character is a frequent accomplice and the girlfriend of Batman's nemesis the Joker, and is also close to Poison Ivy, from whom she gained her immunity to poisons and toxins, as well as her advanced physical abilities.
The character was created by Paul Dini and Bruce Timm and was originally voiced by Arleen Sorkin in Batman: The Animated Series and its tie-ins. The character was portrayed by Hynden Walch on The Batman television series. In the Birds of Prey series, she was portrayed by actress Mia Sara, and by Sherilyn Fenn in the pilot episode. Throughout her portrayals, she is shown to speak with a pronounced Brooklyn accent.
IGN's 2009 list of the Top 100 Comic Book Villains of All Time ranked Harley Quinn as #45.

Origin: Batman: The Animated Series
Harley Quinn first appeared in the Batman: The Animated Series episode "Joker's Favor",[2] as what was originally supposed to be the animated equivalent of a walk-on role; a number of police officers were to be taken hostage by someone jumping out of a cake, and it was decided that to have the Joker do so himself would be too bizarre (although he ended up doing so anyway). Dini thus created a female sidekick for the Joker. Arleen Sorkin, a former star of the soap opera Days of our Lives, appeared in a dream sequence on that series in which she wore a jester costume; Dini used this scene as an inspiration for Quinn.[3] Having been friends with Sorkin since college, he incorporated aspects of her personality into the character.
The 1994 graphic novel Mad Love recounts the character's origin. Told in the style and continuity of Batman: The Animated Series and written and drawn by Dini and Timm, the comic book describes Harley as an Arkham Asylum psychologist who falls for the Joker and becomes his accomplice and on-off sidekick/lover. The story received wide praise[4] and won the Eisner and Harvey Awards for Best Single Issue Comic of the Year. The New Batman Adventures series adapted Mad Love as the episode of the same name in 1999, making it the second "animated style" comic book adapted for the series (the other was Holiday Knights).
She becomes fascinated with the Joker while interning at Arkham, and volunteers to analyze him. She falls hopelessly in love nearly instantly with the Joker during their sessions, and she helps him escape from the asylum more than once. When the Joker is returned to Arkham after a battle with Batman, the sight of her badly injured patient drives Harley to don the costume and become Harley Quinn, the Joker's sidekick and on/off girlfriend. She later becomes fast friends with Poison Ivy, who injects her with antitoxins to give her the same immunity to poisons she has.