The Joker is a fictional character, a supervillain who appears in comic books published by DC Comics. He is the archenemy of Batman, having been directly responsible for numerous tragedies in Batman's life, including the paralysis of Barbara Gordon and the death of Jason Todd, the second Robin. Created by Jerry Robinson, Bill Finger and Bob Kane, the character first appeared in Batman #1 (Spring 1940).

Throughout his comic book appearances, the Joker is portrayed as a master criminal whose characterization has varied. The original and currently dominant image is of a highly intelligent psychopath with a warped, sadistic sense of humor, while other writers have portrayed him as an eccentric prankster. Similarly, throughout the character's long history, there have been several different origin tales; they most commonly depict him as falling into a tank of chemical waste, which bleaches his skin white and turns his hair green and his lips bright red, giving him the appearance of a clown. 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.