The Joker is a fictional character that appears in comic books published by DC Comics. The character first appeared in Batman #1 (Spring 1940), and was created by Bill Finger, Bob Kane and Jerry Robinson. The Joker is a master criminal, whose characterization has varied from a violent sociopath who murders people, causes chaos and commits crimes for his own amusement, to a goofy and virtually harmless trickster-thief. The character is the archenemy of Batman, and has been responsible for numerous tragedies in the Caped Crusader's life, including the murder of Bruce Wayne´s parents, the paralysis of Barbara Gordon (Batgirl/Oracle) and the murder of Jason Todd (the second Robin). Wizard magazine rated Joker as the greatest villain of all time. The Joker's real identity is Jack Dapir according to the first Batman film, but there have been different takes on his origin; the most common variation depicts him as having fallen into a vat of chemicals, which bleached his skin white, dyed his hair green and turned his lips bright red, giving him the appearance of a clown.

The character has appeared in numerous Batman related media; portrayed by Cesar Romero in the 1960s Batman television series; Jack Nicholson in the 1989 film Batman (Nicholson's version of the Joker ranks #45 in the American Film Institute's list of the top 50 film villains); voice actor Mark Hamill in the 1990s Batman: The Animated Series television series; and Heath Ledger in the 2008 Batman Begins sequel, The Dark Knight.