Dr. Harleen Frances Quinzel, better known as Harley Quinn is a super villainess from DC Comics. She is the Joker's self-proclaimed girlfriend and henchwoman. Harley Quinn is eccentric and extravagant, and usually commits crimes with a sadistic glee and hyperactive energy. In most incarnations, she is loyal to the Joker regardless of how cruelly he treats her. Despite being a psychiatrist, Harley is often portrayed as rather dimwitted socially and logically, as she tends to fail to notice obvious problems or overthinks minor issues.
Even though she keeps an enthusiastic, crazed demeanor, deep down she is secretly tormented and tragic. Occasionally, she will have enough of the Joker and being evil and will try to fight on the side of good, such as when the world or someone she truly cares about is at stake. Even when she is on the evil side, she does have a sense of honor.
For example, in the Injustice comic series, she refuses to fight Black Canary when she finds out she is pregnant. Harley also has her limits, and can be pushed too far, even by the Joker, causing her to leave and eventually team up and form a new romance with Poison Ivy.