Joker is a 2019 American psychological thriller film directed by Todd Phillips from a screenplay he co-wrote with Scott Silver. Based on DC Comics characters, it stars Joaquin Phoenix and provides an alternative origin story for the Joker. The film follows Arthur Fleck, a failed clown and aspiring stand-up comedian whose descent into mental illness and nihilism 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 they 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 and was theatrically released in the United States on October 4. It received mixed reviews from critics and was a box office success, setting records for an October release and going on to gross over $1 billion worldwide, becoming the first R-rated film to do so. It held the record for 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 negative reviews and an underwhelming box office performance.