Joaquin Phoenix was reluctant to play "Joker" as he didn't want the film to become a franchise.
The "Gladiator" star is being tipped for an Oscar for his portrayal of the DC Comics villain, but needed convincing to take on the role as he didn't want the film to become a franchise.
Joaquin explained: "I remember, like eight years ago, I was told, 'Movies are changing. They're not making the movies that you want to make, so you've got to do one of these.'
"It makes sense. It probably is a good strategy. But for me, I guess the fear was that you'd get locked into doing something repeatedly that you don't really care about, that doesn't motivate you or excite you."
Director Todd Phillips previously suggested that Joaquin had little interest in the comic book element of the film, which follows how comedian Arthur Fleck transforms into the Gotham City villain who is the archenemy of Batman, who is orphaned billionaire Bruce Wayne.