Dr. Harleen Frances Quinzel, also known as Harley Quinn (a pun on the word "harlequin"), first appeared in the Batman: The Animated Series episode "Joker's Favor", where she served as a humorous female sidekick to the Joker. In her first appearances she was depicted as a character completely devoted to the Joker, totally oblivious to his psychotic nature and obvious lack of affection for her; this characterization has remained more or less consistent throughout her subsequent appearances.
The origin of the character was recounted in a 1994 graphic novelThe Batman Adventures: Mad Love. Told in the style and continuity of Batman: The Animated Series and written and drawn by Paul Dini and Bruce Timm (two of the producers of the animated series and Harley's creators), the comic book reveals Harley's origins as an Arkham Asylum psychiatrist who falls in love with the Joker. The story was widely praised and won the Eisner and Harvey Awards for Best Single Issue Comic of the Year.
The Mad Love story was originally thought too violent for the animated series, but was eventually used in the New Batman Adventures episode "Mad Love" in 1999. This made it the first "animation-style" comic book to be adapted for the series, a practice that would be continued for the episode "Holiday Knights".
Dr. Harleen Quinzel was a psychiatric intern at Arkham Asylum. A model student, in addition to receiving high grades in college, she was also a dedicated gymnast, winning a scholarship to Gotham City University. While researching the lunatics at Arkham, she became fascinated with one particular inmate. Ambitiously volunteering to analyze him, she pleaded with the doctors at Arkham for three months before she could treat him. After he gained her sympathy during their sessions, he seduced her, causing her to fall madly in love with him. After helping him escape from the asylum more than once, Harleen was suspected by the authorities, who revoked her license and placed her in her own cell. During an earthquake in Gotham City, she fled and became Harley Quinn, the sidekick of the Clown Prince of Crime himself.
Quinn's relationship with the Joker is one of the most complex and twisted love affairs in comics: as with all people, the Joker is abusive and manipulative towards Harley, but, just as often, there's evidence of camaraderie, playfulness, and genuine affection towards her. She's the only person who's managed to become intimate on such a long term basis with the Joker, who, in turn, displays occasional moments of confusion and discomfort which results in attempts to kill her.
One time, when the Joker realized he had very deeply hidden feelings of love, he sent Harley off in a rocket.
She crash landed in Robinson Park in the center of Gotham and was found byPoison Ivy. When Harley regained consciousness, Ivy initially planned to kill her. The prospect of her own death totally fails to move Harley, and Ivy is curious as to why. She convinces Harley to tell her story, and soon feels a kinship to her. Considering her another castoff, Ivy offers to help Harley take her revenge on both Batman and the Joker. Ivy took her back to her lair in a toxic waste dump and nursed her back to health. This included injecting Harley with a serum that Ivy had developed which has given Harley immunity to various assorted toxins and Ivy's own poisonous touch and also dramatically enhances Harley's strength and speed. Ivy intends to give her new friend an edge on Batman and the Joker. Quinn and Ivy teamed up and conducted a number of successful capers. Hot-blooded Harley, however, is angrier at the Joker than at Batman, and even initially works with the Dark Knight to help bring down the Clown Prince of Crime.
While Batman eliminates the villain's muscle, Quinn chases the Joker up a damaged building, intending to send him falling to his death. Before she can do so, however, the Joker apologizes. Falling in love with him again, she forgives him on the spot, and serves as his lieutenant throughout the rest of No Man's Land, as well as the Emperor Joker storyline. After this, Ivy dissolved the partnership in disgust. Ivy remains, however, her usual first point of call when she and The Joker are going through a rough patch. Ivy adopted the role of older sister and teller of harsh truths to Quinn about her helpless infatuation with The Joker. She frequently refers to the Joker as "Puddin" and "Mr. J." and she refers to Poison Ivy as "Red" (a reference to her red hair).
In the One Year Later storyline, Harley Quinn resurfaces as an inmate at Arkham Asylum, glimpsed briefly in Detective Comics #823.
Harley next appeared in Batman #663, in which she helps the Joker with a plan to kill all his former henchmen, unaware that the "punchline" to the scheme is her own death. Upon realizing this, she shoots him in the shoulder.
In Birds of Prey #105, Harley Quinn joins the Secret Six as the sixth member. In issue #108, upon hearing that Oracle has sent the Russian authorities footage of teammateDeadshot murdering the Six's employer as payback for double-crossing them, Harley asks, "Is it a bad time to say 'I quit'?"
Harley Quinn has joined forces with Poison Ivy and Catwoman in Gotham City Sirens. Having moved in with Poison Ivy at The Riddler's townhouse, she meets up with Catwoman who offers for the three of them to live and work together. Ivy resolves that she and Harley would provide Catwoman with "positive female reinforcement", and the three then agree to become a team. However, Harley and Ivy have one condition: they demand that Catwoman reveal to them the true identity of the original Batman. Suddenly, however, a new villain who tried to take down Selina Kyle named Boneblaster breaks into the apartment and the three of them have to move after they defeat him.
Later, after a chance encounter with who she thought was Bruce Wayne (but was really disguised Hush), the Joker attempts to kill Harley, apparently out of jealousy. Quinn is rescued by Ivy and Selina, and it is later revealed that her attacker wasn't the real Joker, but one of his old henchmen impersonating him.
During the Holidays, Harley travels to Bensonhurst, Brooklyn, where she visits her family. Her brother seems to be lazy and unwilling to work, causing Harley to fuss at him about the situation. Her mother also voices her disapproval for Harley's status as a wanted criminal, even though her daughter tries to say that she has changed her ways. The meeting leads to Harley going to visit her father in prison. She and her dad talk of why he is in jail once again, and he tries to tell her that he will also change his path if Harley has done so. They share a moment, but Harley realizes that her 'Pop' is trying to find out where she has stashed money away for him. As Harley goes to exit the building, a guard asks for a picture. She tries to refuse, but the guard claims that her father promised she would and he had given him money for the photo: This angers Harley even further.
Quinn soon returns to Gotham City, not wanting to stay anywhere near her family. She then goes back to living with Catwoman and Poison Ivy in an abandoned animal kennel, which she warmly regards as her new home. Following a number of adventures with Catwoman and Ivy, Harley betrays them and breaks into Arkham with the goal of killing the Joker for abusing her as often as he did. However, Harley ultimately chooses to instead release Joker from his cell, and together the two orchestrate a violent takeover of the facility that results in most of the guards and staff members either being killed or taken hostage by the inmates. Harley and the Joker are eventually defeated by Batman and Catwoman, and Harley is last seen being wheeled away while bound in a straightjacket and muzzle. Shortly after this, Poison Ivy breaks into Harley's cell and attempts to kill her for her betrayal, but instead offers to free her if she helps kill Catwoman, who had left both of her fellow Sirens behind in Arkham. Harley agrees, and the two set out to trap Catwoman.
During the ensuing fight, Catwoman says that she saw good in them and really only wanted to help. Just as Batman is about to arrest them, Catwoman helps the two of them escape.