Trivia: The font used for Live With Murray Franklin is identical to the Batman animated series titles. The name of the font is "Plaza," for those that might be curious.
Trivia: While the time period of the movie isn't explicitly stated, the movies showing at the cinema the Waynes are at (Zorro The Gay Blade, Wolfen, Excalibur, and Arthur) were all released in 1981, making that the likely year it's set. The Zorro reference is certainly a nod to established comic continuity, where the Waynes were watching The Mark Of Zorro.
Trivia: Towards the end while Joker is being transported in the police car, the shot of him through the window is similar to one of Heath Ledger's Joker in The Dark Knight.
Trivia: Arthur has a copy of The Blue Boy by Thomas Gainsborough hanging on his wall. The same painting is appreciated by Joker in the 1989 Batman movie.
Trivia: Director Todd Phillips has specifically said that he doesn't see this movie connecting with any other DC movies - it stands alone.
Trivia: The idea of the Joker being a failed stand up comedian comes from famous Joker comic "The Killing Joke", which tells one possible origin story for the character.
Trivia: The person contacting Arthur Fleck on the phone introduces herself as Shirley Wood. Shirley Wood was the name of a talent coordinator for Late Night with Johnny Carson, active in the year depicted in the movie.
Trivia: The final makeup of the Joker was inspired by the serial killer John Wayne Gacy, who went by the name Pogo the Clown. The club Arthur performs at is called Pogo's too.
Trivia: During the riot scene towards the end of the film, the Joker stands up on the car and in the background you can see a billboard for a movie called "Ace in the Hole." This is a line which Heath Ledger's Joker said in the 2008 film "The Dark Knight."
Trivia: Arthur and Sophie go to a diner on Jerome Avenue. The Gotham TV series featured twin brothers, Jerome and Jeremiah, the latter of which ended up becoming the Joker in the series.
Trivia: Joaquin Phoenix won the Oscar for Best Actor for his role in this film. This marked the second time an actor won an Oscar for playing a character that was played previously by another actor that also won an Oscar for their role. The other time was Phoenix's costar in this film, Robert De Niro, winning Best Supporting Actor for playing the younger version of Vito Corleone in "The Godfather Part II," following Marlon Brando winning Best Actor for the first film.
Trivia: The use of "Rock and Roll Part 2" by Gary Glitter within this film caused controversy shortly after the film's release due to the perceived possibility that Glitter, a convicted sex offender, might collect royalties from the song's use in the film. This concern was unfounded, though, since Glitter had long since sold the rights to the song's use; the US rights are currently held by the Universal Music Publishing Group.
Trivia: Actor Justin Theroux has an uncredited cameo as a celebrity guest on Murray Franklin's (Robert DeNiro) TV show.
Trivia: The social worker who talks with Arthur has the last name Kane as a reference to Bob Kane creator of Batman and the Joker.
