The Joker is a fictional character that appears in comic books published by DC Comics. Created by Bill Finger and Bob Kane, with contributions by artist Jerry Robinson, the Joker first appeared in Batman #1 (Spring 1940). In 2006, Wizard magazine rated him the greatest villain of all time. Game Informer asserts that "everyone knows the Joker."

The Joker is the archenemy of the superhero Batman. The Joker is a master criminal with a clown-like appearance, including bleached white skin, red lips, and green hair. Initially portrayed as a violent sociopath who murders people and commits crimes for his own amusement, the Joker, later in the 1940s, began to be written as a goofy trickster-thief. That characterization continued through the late 1950s and 1960s before the character became again depicted as a vicious killer. He has been responsible for numerous tragedies in Batman's life, including the paralysis of Barbara Gordon (Batgirl/Oracle) and the murders of Jason Todd (the second Robin) and Jim Gordon's second wife Sarah Essen.

The Joker was portrayed by various actors in other media. He was portrayed by Cesar Romero in the 1960s Batman television series; Jack Nicholson in the 1989 film Batman; and voice actors Mark Hamill and Kevin Michael Richardson in TV's Batman: The Animated Series and the subsequent The Batman respectively. Nicholson's version of the Joker ranks #45 in the American Film Institute's list of the top 50 film villains. Heath Ledger portrayed the role of Joker for director Christopher Nolan's Batman Begins sequel, The Dark Knight.