Many critics are hailing Thor: Ragnarok as one of the most fun movies in the Marvel Cinematic Universe, due in part to director Taika Waititi's focus on improvisation and comedy. However, during production on the film, actor Mark Ruffalo, who plays Bruce Banner/Hulk, was a little nervous about the movie's departures from previous installments in the MCU.

RELATED: Why Lady Sif Isn't in Thor: Ragnarok

"Do you know how many times I was like, 'are we breaking the Marvel universe,'" Ruffalo told Collider. "We threw everything out. We started all over again with this. We threw the Thor franchise out. We threw everyone's perception of Banner out. We threw everyone's perception of Hulk out. We threw everyone's perception of Thor out. And, yes, we knew what we were doing. At the same time we were like, 'let's just do it, and let's go for it, and let's do it the best and most honest and fun way that we can.' Taika did that, and he wasn't afraid of that... so we improvised a lot and we played... and that playfulness is really appealing on-screen."

RELATED: What The Hela: 15 Things You Must Know About Thor: Ragnarok's Big Bad

Debuting Nov. 3 in North American theaters, director Taika Waititi's Thor: Ragnarok stars Chris Hemsworth as Thor, Tom Hiddleston as Loki, Cate Blanchett as Hela, Idris Elba as Heimdall, Jeff Goldblum as Grandmaster, Tessa Thompson as Valkyrie, Karl Urban as Skurge, Mark Ruffalo as Bruce Banner/Hulk and Anthony Hopkins as Odin.