Harleen Quinzel was a vivcious, likeable,friendly young woman. Beautiful, intelligent and talented, she was however, excluded from the popular social cliques of her school, because there was alaways something a little off-beat, a little whacky and zany about her, that meant she was destined to be somewhat of a loner.She liked the underdogs and "nerds" of her school, but she coudlnt fit in with them either. She was by herself.Full of personality and life, she, however, rarely let anything get her down,although already there was a deep resentment growing within her, at the rejection of her peers, and of her family, who ignored her. She had a great desire to prove herself to them, to make sure noone would ever forget her.After being barred acess to the cheerleader team by the snobs on it, she took up gymnastics, and quickly became a star in that field.Although unafraid of using her sexuality to her advantage, she grew tired of the boys who only used her, and left her if she wouldn't go all the way. In fact, very quickly she was growing tired of the treatment everyone gave her. She knew she was smart. She knew she was attractive. She knew she was talented. And above all, no matter what quirks she had, she knew she was a friendly, and kind person.The desire to prove herself turned into a desire for love.She believed she could get love if she became a star in every way - if she were famous, or highly successful, people would be sure to love her.With this strong will and determination, she got to Gotham Sate Uni on a gymnatsic scholarship, and from there, worked on a Psychology degree, in their prestigious psychology department.
Harley,although determined and quick, could not grasp the conplex theories of psychology, no matter how hard she studied. On top of that, she still had a desire for friends, and so spent many precious moments trying hard to make them, and fit in, once again, facing the rejection of highschool, due to her slightly bizarre nature she was unable to hide. Determined to get her degree, however, she resorted to a last,desperate measure - that of seducing her professor.WELL IT GOT HER THE MARKS DIDN'T IT? She landed her desired job of interning at Arkham Asylum for the Criminally Insane. 
She went ,to the Asylum, full of hope, wanting to help everyone there.Some of the doctors believed her motivations to be less that moral - ie:they thought she wanted to cash in on Arkham's infamous inmates. These theories were erroneous, however, and Harley ignored them.The truth was she wanted to write that book to achieve her long-anticpated goal - fame - and through that, get the love she ached for.Upon her first days, she saw the countless and demented criminals who ravaged Gotham City. Dealing with those sick criminals was all part of the job for Harlene, and she did her best with a hopeless situation.
. The one aspect of her jobwhich disturbed Dr. Quinzel was one particular inmate who was always looking at her more devilishly than the others. It seemed to her like he could read her thoughts, go right inside of her and know all her secrets. She found him hypnotic and bewitching. She knew she was not the only one who felt this, the other doctors and inmates sensed this supernatural air about him too, but it affected her more. Somehow,he always found a way to be in her presence within the hellish gates of Arkham. Finally,she could stand it no more, and requested to have this patient under her charge. The other doctors were wary at first, because this inmate was known for the terrible manipulation ,and torture of his female psychiatrists, but they finally give in. Before starting treatment, she read his case file, she became even more afraid, and felt genuine terror of her patient. In their first session, however, he surprised her by being quiet and gentle.His aura is poetic and hypnotic, and Harlene felt herself being drawn to him. In the weeks that followed, they had long discussions, finding things they have in common, and Dr. Quinzel discovers he has a wonderful sense of humor. He confides in her his own abused childhood,and she feels a terrible rage at this injustice and emotional scarring. He seemed more like her friend than patient, and before she was even aware of what was happening, the sessions turned into counseling for her rather than him. He understood all of her problems, and she let out the torrent of emotion she had been suppressing all those years. She began to see her patient as a kind of God, her savior, an angel who has been terribly misunderstood by the world. What was once fear of him, turned into an obsession with her patient : The Joker.
She has allowed the Joker to manipulate her for so long, she believes almost anything he says.. She is completely unaware that the childhood he told her about is false, and that he is using her for his own ends - to him she is nothing more than an experiment to see if he could turn a strong, independent woman into a weak, dependent worshipper of himself.Seeing that he has succeeded, and that the only thing left to be done is completely snap the last of her sanity, the Joker decides that can wait until another time, he is bored in the asylum, so he breaks out. For one week he continues on a crime spree of murder, with Harlene sitting anxiously back at the asylum, believing him to be scared and unsure of what was going on.. Batman apprehends the Joker, and takes him back to the asylum. The two had been in a fight, and Batman triumphed. The Joker is barely conscious as Batman leads him down the corridor, and Harleen rushes out to receive her patient. Seeing the state he is in, the whole world seems to stop for Harleen. There is a roaring in her ears as she rushes to take Joker in her arms. She is unaware of the stares of the doctors, Batman's shocked face, or the tears streaming down her cheeks, and she does not hear her own scream as the asylum's hospital staff take the Joker from her.
. She rushes home and gets together an assortment of equipment, including an appropriate costume to suit her new persona. That night, she breaks the Joker out of the asylum, and they drive off into the sunrise, the Joker screaming laughter all the way. When they stop, the Joker leans over to kiss her, and in that kiss, Harleen completely lost the little touch with reality she had left and became Harley Quinn.
To make sure she never goes back to what she was, the Joker continues to twist her mind, convincing her all the terrible things he does are 'just a joke', keeping her drugged on love for him. He confuses and bewilders her, physically and emotionally abusing her, and then comforting her. 
Her sick infatuation with him leads her to carry out his every beck and call. She is enthralled with his maniacal life of crime, chaos and murder.
She harbors fantasies that once the Dark Knight is dead, she and her " Puddin' " will get married,have children and live happily ever after. To her, Joker is her Lover, Boyfriend, Best Friend, Confidante, Teacher, Mentor, Father and God.
The Joker is amused by her undying devotion, and views her as a kind of pet, a sex toy and a handy assistant in crime. Harley is truly the only person to see below his demented exterior to the hurting man deep within the Joker. She believes Batman is the source of his pain, and she is a deadly enemy to the Dark Knight. Underneath her demented exterior, she is sweet and loveable.
Her trademark is her Joker wand, which is a grapple, a gun,,and a knife.
When apprehended, she is returned to Arkham as a patient, not the respected doctor she once was.