The Joker is a fictional character, a comic book supervillain appearing in publications by DC Comics. The character was created by Jerry Robinson, Bill Finger and Bob Kane, and first appeared in Batman #1 (Spring 1940). As the archenemy of the superhero Batman, the Joker has subsequently appeared in television programs, films, games, and on a variety of merchandise. The credit for creating the character is disputed, with both Kane and Robinson claiming responsibility for the Joker's design, but acknowledging Finger's writing contribution.

Throughout his comic book appearances, the Joker is portrayed as a highly intelligent, master criminal. Originally introduced as a psychopath with a warped, sadistic sense of humor, the character became a goofy prankster in the late 1950s in response to the regulation of the Comics Code Authority, before returning to his darker roots in the early 1970s. As Batman's nemesis, Joker has been a part of many of the defining stories of that character, including the paralysis of Batman's ally Batgirl, and the murder of Jason Todd, Batman's ward and the second Robin. Throughout the Joker's long history, there have been several different origin tales, but the most common has falling into a tank of chemical waste, which bleaches his skin white and turns his hair green and his lips bright red. He has been repeatedly analyzed by critics as the perfect adversary for Batman; their long, dynamic relationship often parallels the concept of yin and yang.

As one of the most iconic and recognized villains in popular media, the Joker was ranked #1 on Wizard's list of the 100 Greatest Villains of All Time.