Dr Harleen Quinnzel, a doctor in Arkham Asylum had an interst in extreme personalities, and The Joker definitly fit that description. He left a bunch of flowers on her desk. She asked him why he'd been out of his cell. He replied with that if she wanted to tell she already would have. Harleen decided to schedule an apointment with him and discovered his dark past. He even charmed her. Very unprofessionally, she fell in love with The Joker. One week he escaped Arkham and came back the week after with a black eye, several dcars and a broken arm. This was it for Harleen. She mentally snapped at that moment and became crazy. She stole a harlequin costume and broke Joker out of Arkham, and has since been his henchwoman and girlfriend.