Which movie(s) inspired the 2019 DC comic movie Joker?

The movie Joker is heavily influenced by 1970-1980 Martin Scorsese movies such as the The King of Comedy and Taxi Driver, the former of which is one of Scorseses' least-known movies. The titular character, Joker, is also created based on studies of mentally-ill main characters from the above-mentioned movies, Rupert Pupkin and Travis Bickle. The lead actor of both Scorsese movies, Robert De Niro, even played a role in Joker to pay homage to Rupert Pupkin.