Harley Quinn, real name Harleen Quinzel, is a villain, occasional anti-hero, and member of the Gotham City-based criminal group known as the Suicide Squad. She is best known for her relationship with the Joker, with whom she has had a tumultuous on-off relationship. Harley Quinn is known for her multiple personalities due to her traumatic experiences and conditioning by the Joker, which makes her a unique and unpredictable character. She is frequently portrayed as having a split personality and struggling with mental health issues.