Harley’s origin was, for years, identical in the comics to the one seen in the Batman animated series.
But, in the comic series Harley Quinn, a quite different one was established.
Born Harleen Quinzel, Harley’s mother is a somewhat harsh, but forgiving lady, who constantly calls Harley evil and compares her to other heroes. Harley’s younger brother is a dead beat with children from at least two different women and still lives in his mothers house. Harley apparently sent him several large sums of money to get his life on track, but he squandered it. Harley’s father is a criminal con-man, known for swindling women out of their money with his charm. Harley states that the main reason she became a psychiatrist was so she could understand why her father did what he did to their family.
Harley went to study psychology, but found doing so dull. She tricked her way in to a college.
She came up with a theory about being in love having similarities with being a criminal. About, how far can someone go for love and decided to use her boyfriend, Guy, as the test subject, pretending that she had committed various crimes, such as murdering a teacher, to Guy’s surprise. Thinking he was looking out for Harley he shoots an innocent man believing him to be “murdered” professor who hadn’t died yet.
Guy thinks that he can`t live with the guilt, and wants to die, but can’t bring himself to suicide and asks Harley to kill him instead. And she does, for love, disguising the murder as a suicide.
Traumatized by these events, she begins to believe that universe is in a constant state of chaos, like Guy thought. She represses her feelings of sorrow, and feels connected with the Joker, who believes in some of the same things as Guy, and so finds a job at Arkham Asylum, demanding to speak to him.
During the very first session, she shows the Joker her blossoming insanity, and obsession towards him. Joker finds this appealing, and Harley helps him escape various times, before eventually becoming his henchgirl.
Eventually Harley was caught by Batman and put into a cell in Arkham – she is able to escape time and time again. During the events of No Man’s Land she is finally able to escape, immediately choosing to rejoin with the Joker and help him in his crimes. Later, in another retelling of her origin it is explained that she was a psychology student working part time as a stripper to pay her bills.
She lies about Joker having seduced her, and making her gradually insane, later on.