Harley Quinn

Batman Death Waltz
Dr. Harleen Quinzel is a psychiatric intern at Arkham Asylum. A model student, in addition to receiving high grades in college, she was also a dedicated gymnast, winning a scholarship to Gotham City University. While researching the lunatics at Arkham, she became fascinated with one particular inmate. Ambitiously volunteering to analyze him, she pleaded with the doctors at Arkham for three months before she could treat him. And the more she treated The Joker, the more she broke rules in order to become closer to him.

Becoming Harley Quinn
The Joker eventually broke out of Arkham Asylum. However before he left, he tortured Harleen, gassing her with laughing gas. After the incident she found herself trying to get his attention more on the outside. Until he finally gave her a chance to prove her love to him. In the end she released the 'super criminals' from their cells at Arkham. Completely leaving her old life behind, becoming Harley Quinn.