Harleen Quinzel (Earth-4678)

"Well, look who's too late to save the day. How's it going, Bat-brain? It's been a while."

- Harley Quinn, to Batman

Dr. Harleen Quinzel was an Arkham Asylum psychiatrist, who begged and eventually convinced her superiors to treat the Joker, became obsessively fixated on her patient, and believed herself to be in love with him. She helped him escape from confinement and took on her own criminal identity as Harley Quinn. Quinn was a violent and unpredictable felon whose only motivation, beyond general mayhem, was achieving the Joker’s approval. Because of the Joker's cruel and mercurial nature, this in some ways made Quinn just another one of his victims - albeit a very dangerous one.

Source

 * https://arkhamcity.fandom.com/wiki/Harley_Quinn