Harley

From a young age, Harleen Quinzel was obsessed with psychological issues, due to her father's own struggles with his mental health. After graduating from Gotham State University as a Doctor of Psychiatry, she was placed in both Arkham Asylum and Blackgate Prison where she interviewed a number of inmates, including the mysterious "John Doe" and Oswald Cobblepot.

Over time, despite the help she offered to her father, he committed suicide some time after the riots at Arkham and Harley learned the mental illness he had was also hereditary. Whether it was a result of the trauma of losing her father and knowing she would suffer the same mental illness or the beginning stages of the illness itself, Harley suffered a mental breakdown and quit her job. Her eagerness to cure her hereditary illness made her an easy target for the Riddler, Gotham's original super-villain, who recently returned to the city to finish recruiting individuals to complete his criminal organization, The Pact.

When Riddler revealed that he was planning an attack on the organization SANCTUS to retrieve the experimental virus, Project LOTUS, Harley was easily drawn into his fold, knowing of LOTUS's regenerative capabilities, which she could use to cure her hereditary illness. However, Riddler, who truly lusted for revenge over SANCTUS and the Agency, did not inform Harley that LOTUS would only make her condition worse, knowing she would not agree to his plans if she had such information. Renaming herself as Harley Quinn, Harleen became a criminal and also recruited her former patient, John Doe, into the Pact as well, knowing of John's potential to incite violence and chaos from their previous therapy sessions, after he was legally discharged from Arkham Asylum.

Despite the group being founded and led by the Riddler, Harley and the others worried about his choice to draw Batman's attention, due to the possible risk of exposure.

Though initially a calm and collected young doctor, Harley's breakdown caused her to look for excitement wherever possible. She seemed to have an enjoyment for chaos and trouble, choosing to start fights or threaten others at seemingly random times. Harley seemed to be unstable, but it remains unknown whether this was put on to throw off the other members of the Pact, making sure she was never taken advantage of, or part of the aftereffects of the breakdown. Harley also seemed to suffer from violent outbursts whenever something didn't go her way, which made her all the more dangerous when stirring up chaos around her.

Sledgehammer/Mallet: Harley would often carry a large sledgehammer with her at all times, often to destroy objects or cause trouble. Though a very deadly weapon, Harley was able to hit it with enough force to knock someone unconscious and not kill anyone. This was often her preferred weapon in close-quarters combat and whilst on riots with the Pact. If Harley is captured by the Agency, she is later given a new mallet with an electroshock feature, allowing her to stun her opponents. Pistol: Harley would use a customized pistol whist out in action, though it is unclear how often she used it. The pistol seemed to be used whenever she wished to kill someone and in battles where close quarters was not a viable option. Mannequin Bombs: During the confrontation at the Gotham Bridge, Harley used mannequin heads stuffed with C4 explosives. The bombs were quite destructive, being able to cause structural damage to the location when detonated. Quinn also rigged them to a dead-man switch, which would detonate them if she released the switch under any circumstance. The bombs would later inspire "John" to create more when he became the Joker.

Harley is a lean white Caucasian-American woman with blue eyes and a blonde shoulder-length hairstyle which she has partially dyed in red and black. Harley has considerably large breasts, a small waist, and rather wide hips. She regularly coats black mascara around her eyes in the shapes of diamonds in keeping with her overall diamond theme and she also wears red lipstick.

She wears a short black leather biker jacket over a skintight red and black corset set in a diamond pattern. Red latex gloves. And skin-tight latex pants complete with a black and red diamond-styled belt and black combat boots with red and black diamonds encrusted on them.