Joaquin Phoenix was pretty hard on himself while making Joker. Director/writer Todd Phillips states that Phoenix would often walk off the set. However, he would always come back with the intention of topping what he had done before. Phoenix had a tough time as he saw the character he originally signed on to play change and evolve as the production went on, which meant that he had to adapt along with the fictional Arthur Fleck to keep up. In the end, the character he originally set out to play ended up as a completely different person.

In a new interview, Todd Phillips was asked what it was like working with Joaquin Phoenix. The actor has been known to be difficult to work with at times and he lived up to his reputation while working on Joker. But, according to Phillips, that's what makes Phoenix such a great actor. Phillips had this to say about working with Phoenix.

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"In the middle of the scene, he'll just walk away and walk out. And the poor other actor thinks it's them and it was never them - it was always him, and he just wasn't feeling it... If he goes on Jimmy Kimmel and walks off after two minutes, I'd be like, 'That's my boy.'"

With that being said, Joaquin Phoenix never walked out when he was working with Robert De Niro on Joker. De Niro was impressed with what he saw when working on the movie and notes, "Joaquin was very intense in what he was doing, as it should be, as he should be." The two struck up an instant working relationship centered on getting the work done in the best way possible.

Todd Phillips and Joaquin Phoenix worked together for months before the production started on Joker. They got into heated discussions about every little detail of the character, down to how much he should weigh. When it came down to it, Phoenix wanted to play Arthur Fleck at a normal weight, while Phillips wanted the character to be super skinny. In the end, the director won and Phoenix dropped 52 pounds to get into character. He also learned how to apply his own clown makeup and started a journal, which he filled with one-liners and jokes that appear in the movie.

Joaquin Phoenix and Todd Phillips took a long time to craft the Joker standalone movie, and it appears all of their hard work has paid off. Before Phoenix had officially signed on to do the movie, it was rumored that Leonard DiCaprio was going to play the Clown Prince of Crime. However, that appears to be false as Phillips says the movie was written for Phoenix. Whatever the case may be, Joker has been getting heaps of praise from critics who have seen the early screenings. The interview with Todd Phillips was originally conducted by New York Times.