Phoenix lost an astonishing 52 pounds for the role, a process which he said helped him get into the right headspace to play Joker, but which also took a mental toll. "It turns out that affects your psychology," he told The Hollywood Reporter at the Venice Film Festival. "You start to go mad."
Undergoing a drastic physical change seems to have become the norm since Heath Ledger delivered his deeply sinister, Oscar-winning turn as the villain in The Dark Knight, after a broader performance by Nicholson in Batman. More recently, Jared Leto set another precedent for Phoenix and slimmed down dramatically to play a lean, mean version of Joker in 2016's Suicide Squad.
Unlike other movies and TV shows which feature the clown prince of crime, Joker is an origin story, set in 1981 Gotham City, and follows the transformation of Arthur Fleck (Phoenix) from a down on his luck comedian to a dangerous criminal. While the character has famously gone without a backstory for most of his appearances in print and on screen, Todd Phillips' film gives Fleck an unspecified brain injury, one symptom of which is fits of uncontrollable laughter.
"He’s so hard to define and you don’t really want to define him," said Phoenix. "We would get close at times where I found that I would identify certain parts of his personality or his motivation, and then I would back away from that because I wanted there to be a mystery to the character. Throughout the course of shooting it felt like every day we were discovering new parts of his personality, up until the very last day."
"It was his struggle to find happiness and to feel connected and to feel warmth and love, and that’s the part of the character I was interested in. He was so many different things to me. Who he was in the first few weeks of shooting was completely different than who he was in the end. He was constantly evolving. I’ve never had an experience like this. The more unpredictable and looser we left it, the more exciting it was."
See the full trailer for his transformation below.
This article originally appeared on Men's Health