Joaquin Phoenix is not the easiest actor to sign onto just any project. He's thoughtful and precise when it comes to choosing projects, and he's not too crazy about big studio movies. The Oscar-nominated performer has notoriously flirted with a few big projects in the past only to ultimately decline to be involved—most notably Marvel’s Doctor Strange, in which he would have played the title character. So it was somewhat surprising when we learned that he would be leading Joker for Warner Bros., which seemed a bit out of character for the Inherent Vice and The Sisters Brothers actor.

And Phoenix admits he certainly had his reservations at first. Speaking with TotalFilm, the actor says it took him a while to commit, explaining why he was hesitant:

“It took me a while [to commit]. Now, when I look back, I don’t understand why… There was a lot of fear, yeah. But I always say there’s motivating fear and debilitating fear. There’s the fear where you cannot make a fucking step, and there’s the kind where it’s like, ‘OK, what do we do? That’s not good enough.’ And you’re digging deeper and deeper. I love that kind of fear. It guides us, makes us work harder.”

There was another reason Phoenix was hesitant, and it has to do with the way superhero or comic book movies are usually told:

“I think oftentimes, in these movies, we have these simplified, reductive archetypes, and that allows for the audience to be distant from the character, just like we would do in real life, where it’s easy to label somebody as evil, and therefore say, ‘Well, I’m not that.’”

But co-writer/director Todd Phillips’ vision for Joker was to eschew traditional comic book storytelling (he previously revealed Joker pulls nothing from the comic books) in favor of crafting an introspective character piece, which ultimately appealed to Phoenix:

“And yet we all are guilty. We all have sinned. And I thought that here was this film, and these characters, where it wouldn’t be easy for you as an audience. There are times where you’re going to feel yourself connected to him, and rooting for him, and times when you should be repulsed by him. And I like that idea of challenging the audience, and challenging myself to explore a character like that. It’s rare to explore characters like that in any movies, but specifically in the superhero genre.”

In discussing Phoenix’s casting, Phillips put it rather succinctly:

“The goal was never to introduce Joaquin Phoenix into the comic book movie universe. The goal was to introduce comic book movies into the Joaquin Phoenix universe.”

What, exactly, does that look like? We’ll find out when Joker hits theaters on October 4th, but before then the film is playing the fall film festival circuit at Venice and TIFF, so look for the first reviews in the next few weeks—including right here on Collider.