Joker is a 2019 American psychological thriller film directed by Todd Phillips from a screenplay he co-wrote with Scott Silver. The film stars Joaquin Phoenix and is loosely based on DC Comics characters, including the Joker. It follows Arthur Fleck, a failed clown and aspiring stand-up comedian whose descent into mental illness and nihilism culminates with the emergence of an alter-ego known as "Joker" and inspires a violent countercultural revolution against the wealthy in a decaying Gotham City. Robert De Niro, Zazie Beetz, and Frances Conroy appear in supporting roles. Distributed by Warner Bros. Pictures, Joker was produced by Warner Bros. Pictures and DC Films in association with Village Roadshow Pictures, Bron Creative and Joint Effort.

Phillips conceived Joker in 2016 and wrote the script with Silver throughout 2017. The two were inspired by 1970s character studies and the films of Martin Scorsese, particularly Taxi Driver (1976) and The King of Comedy (1982); Scorsese was initially attached to the project as a producer. The film loosely adapts plot elements from Batman: The Killing Joke (1988) and The Dark Knight Returns (1986), but Phillips and Silver otherwise did not look to specific comics for inspiration, nor did he wish for it to be connected to any prior Batman film continuity. Phoenix became attached in February 2018 and was cast that July, while the majority of the cast signed on by August. Principal photography took place in New York City, Jersey City and Newark, from September to December 2018. Joker is the first live-action theatrical Batman film to receive an R rating from the Motion Picture Association.

Joker premiered at the 76th Venice International Film Festival on August 31, 2019, where it won the Golden Lion, and was theatrically released in the United States on October 4. The film's critical reception was mixed but was a box office success and set records for an October release. It grossed over $1 billion, becoming the first R-rated film to do so, and it was the highest-grossing R-rated film until being surpassed by Deadpool & Wolverine in 2024. It was also the sixth-highest-grossing film of 2019 and received numerous accolades. A sequel, Joker: Folie à Deux, was released on October 4, 2024, to commercial and critical failure.