Originally Warner Brothers wanted Martin Scorsese to make this film with Leonardo DiCaprio as Arthur and Robert De Niro to play Murray Franklin. However in the end this proved to be logistically impossible as DiCaprio had already signed on to do Once Upon a Time... in Hollywood (2019) for Quentin Tarantino which was due to start filming at the same time. Scorsese had also committed himself to another project, The Irishman (2019), which also starred De Niro. However De Niro himself had just finished filming his scenes for that film by the time Joker went into production so was able to commit himself to doing this film too. See more

Goofs

When Arthur kills the three men in the subway, he fires eight shots without reloading his gun. Inside the car, he shoots the first man in the head, the second man twice in the chest, and the third man in the leg. After they leave the car, he shoots him once in the back, then approaches him, and shoots him three more times. A .38 revolver holds only 6 bullets.However, as it has been shown that Arthur remembers things differently than how they occurred (such as the comedy club scene), it could be possible that Arthur either remembers things differently from how they actually occurred, or that it did not happen at all and is all happening in his head. See more