Harley Quinn is a major character in the DC Extended Universe.
She appears as the deuteragonist in Suicide Squad, the titular main protagonist of Birds of Prey (And the Fantabulous Emancipation of One Harley Quinn) and the tritagonist in The Suicide Squad.
She was originally the Joker's psychiatrist, however, as time went on, she fell in love with him and helped him escape from Arkham Asylum. Since then, she teamed up with him and become his partner in crime before being kicked out by him, leading her to make her own way and renounce him.
She is portrayed by Margot Robbie.