The Joker is a supervillain appearing in American comic books published by DC Comics. Created by Bill Finger, Bob Kane, and Jerry Robinson, the character first appeared in the debut issue of the comic book Batman on April 25, 1940. Credit for the Joker's creation is disputed; Kane and Robinson claimed responsibility for his design while acknowledging Finger's writing contribution. Although the Joker was planned to be killed off during his initial appearance, he was spared by editorial intervention, allowing the character to endure as the archenemy of the superhero Batman. In the DC Universe, the Joker is portrayed as a criminal mastermind and the antithesis of Batman in personality and appearance. He was introduced as a psychopath with a warped, sadistic sense of humor but became a comical prankster in the late 1950s in response to regulation by the Comics Code Authority, before returning to his darker roots during the early 1970s. The Joker has been part of defining Batman stories, including the murder of Jason Todd—the second Robin and Batman's ward—in "A Death in the Family" (1988) and the paralysis of Barbara Gordon—the first Batgirl—in The Killing Joke (1988). Unlike many comic book characters, the Joker does not have a definitive origin story, but various possible ones have been developed. The most common story involves him falling into a tank of chemical waste that bleaches his skin white, turns his hair green and lips red, and leaves him with a rictus grin; the resulting disfigurement drives him insane. The Joker possesses no superhuman abilities, instead using his expertise in chemical engineering to develop poisonous or lethal concoctions and thematic weaponry, including razor-tipped playing cards, deadly joy buzzers, and acid-spraying lapel flowers. The Joker sometimes works with other Gotham City supervillains, such as the Penguin and Two-Face, and groups like the Injustice Gang and Injustice League, but these partnerships often collapse due to the Joker's desire for unbridled chaos. A romantic interest and sidekick for the Joker, his former psychiatrist Harley Quinn, was introduced in the 1990s. Although his primary obsession is Batman, the Joker has also fought other heroes, including Superman and Wonder Woman. One of the most recognized characters in popular culture, the Joker has been listed among the greatest comic book villains and fictional characters ever created. His likeness has appeared on merchandise such as clothing and collectible items, and he has inspired real-world structures (such as theme park attractions) and been referenced in various media. The Joker has been adapted in live-action, animated, and video game incarnations.