The actor challenged himself physically, mentally, and emotionally to bring us the best screen performance of 2019.

Although Phoenix famously didn't look to any previous screen interpretations of the Joker—including Heath Ledger's—in crafting his performance, he did share one aspect of the late "Dark Knight" star's approach to the role.

Phoenix found himself very isolated while shooting the film, for a couple of reasons.

For one, it was difficult for him to simply turn off Arthur Fleck at the end of the day.

"Man, you know what I'm talking about, it's so hard to just try to be happy all the time."

In an interview with Metro, the actor said, "At the end of the night there was never really an end."

"It stayed with me every night after work for another two or three hours."

"I never felt this moment of being done with my work day [...] I didn't socialize at all."

"The person I interacted with was director Todd Phillips."

"That became my world."

"It was nonstop."

Phoenix also revealed that as a by-product of his own strict diet, his opportunities to interact with the cast and crew were even more limited than they might otherwise have been.

He said, "I also didn't really have a life at that time because I couldn't go out to eat."

Fortunately, the role was simply so stimulating for Phoenix that he actually found these conditions to be agreeable.

He said, "I want to say it was super hard."

"But it was so inspiring, that as much energy I put into it, it gave it back."

"I would go home after work and we would just talk about the next scene."

"I was just super excited."

"I would show up at set two hours early to just sit in the trailer and talk about it."

Phoenix famously lost over 50 pounds for the role of Arthur Fleck.

In a wide-ranging talk with USA Today about "Joker," he revealed that he subsisted largely on a diet of steamed green beans, apples, and lettuce during the shoot.

This was nothing new.

He had lost a similar amount of weight for his role in Paul Thomas Anderson's acclaimed 2012 drama "The Master."

Just because he had done it before, though, doesn't mean that he was in any way keen to repeat the experience.

Phoenix, who disclosed that the same nutritionist tasked with whittling him down for "The Master," returned to torment him further for "Joker," said, "In all honesty, I didn't want to do it again."

"It's a horrible, brutal diet, but you get all the vitamins and minerals, so you're like safe."

"It's grotesque."

Phoenix has been open about the fact that the dramatic weight loss had a profound effect on his mental state, and that he was able to use the psychological difficulty it presented to inform his acting in Joker.

If he had been able to have it his way, though, Arthur wouldn't have been the rail-thin, emaciated figure we see in the film.

In an interview a month before the film's release, the actor told the New York Times, "I thought he should be kind of heavy."

"Todd was like, 'I think you should do the real thin person.'"

His assessment of the experience didn't soften over the months after "Joker" hit theaters.

He told the Times that sticking to the diet was, quote, "a horrible way to live."

Finding his version of the Joker's famous cackle was a particularly daunting task for Phoenix, as the film posited a unique take on that particular trait.

Arthur's laughter is pathological, a disorder which causes him to burst into violent, uncontrollable laughter at the most inappropriate of times.

Part of Phoenix's method for perfecting his version of the Joker's laugh was to study videos of real-life mental patients afflicted with this disorder.

For a time, the actor was reluctant to employ the laughter, as he simply wasn't confident that he'd nailed it.

He explained, "I think Joker is a part of Arthur that's trying to emerge, and I think that was a really interesting way of looking at this laugh."

"But honestly, I didn't think that I could do it."

"I would practice alone, and then asked Todd to come over to audition my laugh, because I felt like I had to do it on the spot and in front of somebody else."

"It took me a long time."

Phoenix has even said that, to a large extent, he's still not sure if he got it exactly right except in a few instances.

Speaking with ETOnline, he said, "I thought at some point that it would become easier, but I don't think it did."

"I think it became more difficult, actually."

The actor went on to explain that while it worked for some scenes, others were, quote, "a struggle," saying: "Sometimes one take would work and another wouldn't."

"It just was I think something that was alive, in a way."

Perhaps the biggest challenge for Phoenix in preparing to play Arthur Fleck was also, in large part, what drew him to the role: an extreme sense of uncertainty.

In the USA Today interview, the actor explained that the character has an innate sense of slipperiness to his identity, a resolute unwillingness to allow himself to be pinned down as any one archetype.

This quality exhibited itself not only on the pages of the screenplay, but on set, as Arthur's characterization morphed and evolved throughout "Joker's" shoot.

Phoenix said: "When we were prepping for it, I felt very frustrated because I couldn't lock on anything that felt like a foundation for the character."

"And at some point, I realized that was the f--ing point."

"He was unstable."

"Gary, you were the only one who was ever nice to me."

Eventually, though, Phoenix along with Phillips and the rest of "Joker's" cast and crew found that this grey area was exactly where they needed to be.

He said, "It's shaky ground as an actor."

"I enjoy not knowing precisely what a character may do, but you want to have like a couple moments that you feel solid about."

"And that never really happened."

"We just became very comfortable with not knowing."

It was a singularly unique approach which led to a singularly unique performance, one which finally netted Phoenix that golden statue which he probably should have been awarded years ago.

In his acceptance speech, he told his peers, "We share the same love that's the love of film."

"And this form of expression has given me the most extraordinary life."

"I don't know where I'd be without it."

It's only fitting that this is so, because Phoenix has given us nothing but extraordinary performances and with "Joker," an all-time great one.

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