Mad love (First edition.)

Harleen Quinzel grew up in an abusive household with a criminal and became a psychologist to deal with her own broken family.

At Arkham Asylum, she attempted to treat the Joker and instead fell hopelessly in love with him, helping him escape and becoming a member of his organization.

Quinzel became Harley Quinn, a bizarre contradiction of violence and mercy.

She blames Batman for her inability to maintain a stable relationship with the arch-villain, and that causes her to have an abiding hatred for the hero, who she seeks to kill.