Joker

Jack Napier is mob boss Carl Grissom's right-hand man and is having an affair with Grissom's mistress. Grissom sets him up to be killed by police at Axis Chemicals. Fighting Batman, Napier falls into a vat of chemicals and comes out with white skin, green hair and a permanent grin. He kills Grissom, takes over the gang and calls himself the Joker.

The Joker poisons beauty products with Smylex gas, which makes people die laughing, trashes a museum and becomes obsessed with photographer Vicki Vale. At Gotham's bicentennial parade, he hands out cash while giant balloons release the gas, but Batman hauls the balloons away. Atop the cathedral, Bruce realizes Napier was the mugger who killed his parents years before. The Joker tries to escape by helicopter, but Batman ties his leg to a stone gargoyle, and he falls to his death.

Gotham, 1981. Arthur Fleck is a clown for hire who lives with his mother, Penny, and dreams of doing stand-up. A condition makes him laugh uncontrollably at the worst moments. After a beating on the street, a coworker gives him a revolver. On the subway, in clown makeup, he kills three Wayne Investments employees who attack him, and the killings spark clown-mask protests.

Off his medication, Arthur comes to believe he's Thomas Wayne's son, until he learns his mother lied and let him be abused as a child. He kills Penny and realizes his romance with neighbor Sophie existed only in his head. Talk show host Murray Franklin mocks a clip of him and invites him on. Live on air, Arthur asks to be introduced as Joker, confesses to the subway killings and shoots Murray. In the riots that follow, the crowd cheers him, and a rioter kills Thomas and Martha Wayne. At the end, Arthur is in Arkham, leaving bloody footprints.

Two years later, Arthur awaits trial at Arkham State Hospital. His lawyer wants to prove the Joker is a separate personality. In a music class he meets Lee Quinzel, who says she admires him, and they share a romance full of imagined musical numbers. Lee says she's pregnant.

At trial, Arthur fires his lawyer and represents himself in Joker makeup. After a guard kills a young inmate, he renounces the persona on the stand. The jury finds him guilty, and a bomb outside scars prosecutor Harvey Dent's face. Arthur escapes but rejects the fans who only want the Joker. Lee leaves him on the stairs. Back in Arkham, another inmate tells Arthur a joke and stabs him to death. As Arthur dies, the young man carves a smile into his own face.

Heath Ledger's Joker debuts robbing a mob bank with a crew who kill each other off one by one. The card left at the end of Batman Begins already announced him. He offers the bosses to kill Batman for half their money. He gives different versions of how he got his scars and kills a judge and the police commissioner to force Batman to unmask.

Caught after attacking Harvey Dent's convoy, he runs everything from inside the police station. He puts Rachel Dawes and Dent in buildings rigged with bombs, swaps the addresses on Batman and escapes as Rachel dies. Then he burns the mob's mountain of cash, visits Dent in the hospital and pushes him toward revenge. Dent walks out as Two-Face, and the hospital blows up.

For his finale, the Joker rigs two ferries with bombs, one full of citizens and one full of prisoners, and gives each the other's detonator. If nobody presses the button by midnight, he'll blow up both. The passengers refuse to kill each other.

Batman finds him in a building under construction and takes him down. Hanging upside down, the Joker says they're destined to do this forever and that he's already won the bet: he corrupted Harvey Dent. The police take him away.

At the end of The Batman, Edward Nashton, the Riddler, sits dejected in a cell at Arkham State Hospital. Next door, an inmate we never see clearly strikes up a conversation, laughs and comforts him. He's Barry Keoghan, credited as "Unseen Arkham Prisoner", and Matt Reeves confirmed he's the Joker.

A deleted scene, later released by the studio, shows Batman visiting this prisoner in Arkham for help understanding the Riddler. His face is blurred and covered in scars.

The Joker was created by Bill Finger, Bob Kane and Jerry Robinson and debuted in Batman #1 in 1940. His grin came from Conrad Veidt in The Man Who Laughs (1928). Alan Moore's The Killing Joke imagines a failed comedian who falls into a chemical vat, and the Joker himself says he'd rather his past be multiple choice.