'Harleen Frances Quinzel' aka 'Harley Quinn' was created by Paul Dini and Bruce Timm, debuting in "Batman: The Animated Series" (1992).
The character later appeared in DC Comics' "Batman" comic books, debuting in "The Batman Adventures" #12 (1993)
"...in 'Suicide Squad', flashbacks reveal that psychiatrist 'Dr. Harleen Quinzel' fell in love with the psychopathic supervillain 'Joker', during his time as her patient at 'Arkham Asylum'.
"Joker manages to convince Dr. Quinzel to free him, and after his men take over the asylum, he gives her electroshock therapy.
"Quinzel then willingly jumps into chemicals that created Joker, at the 'Ace Chemicals' plant, bleaching her skin and completing her transformation into 'Harley Quinn'.