Trivia: SPOILERS: Director Todd Phillips has defended the controversial ending, in which it is revealed that Arthur is not the Joker who would go on to fight Batman when he is stabbed and killed by another inmate, who then carves a smile onto his face. Phillips noted that the two films were called "Joker," and not "THE Joker," and stated that Arthur was the person who inspired the real Joker—presumably the inmate who killed him. However, this explanation was poorly received by fans, who felt duped.
Trivia: The first time Maika Monroe saw Nicolas Cage in make-up as Longlegs, her heart rate jumped up to over 170 bpm, around 100 above her resting heart rate.
Trivia: Near the beginning of the movie, as the SWAT vehicles are approaching, a billboard is visible in the background advertising the movie "The Watchers", which was directed by M. Night Shyamalan's daughter, Ishana.