Robert Downey Jr. Praises 'Bangable' Mark Ruffalo's Poor Things Nude Scene

The pair sat down for Variety's Actors on Actors interview special, where they took a trip down memory lane, dishing on how they first met to working alongside each other in the Marvel Cinematic Universe -- and some of the epic body transformations they've undergone along the way.

In their roles in the Avengers saga, Downey Jr. as Tony Stark in Iron Man, and Ruffalo as Bruce Banner a.k.a. The Hulk, they were forced to undergo extreme diets and fitness regimens to portray the super heroes -- something Downey Jr. recalled Ruffalo was not a huge fan of.

"On one of these Avengers movies, you take off your shirt, and you were in really good shape," Downey Jr. remembers. "And the director was like, 'We got it,' and you're like, 'Oh, can I please stop dieting and working out now?'"

While the Oppenheimer actor could seemingly relate, he also had high praise for Ruffalo who he applauded for not being "vain," despite his clearly "bangable" body.

Downey Jr. continues, "There is no one I've ever come across who is more anxious to not be vain past the point where it is necessary to achieve an end for their work."

While it's perhaps the roles they're known best for, they've each shape-shifted for other parts, with Downey Jr. filling in his earring hole to play Lewis Strauss in the Christopher Nolan film and Ruffalo donning ass pads for his part in the fantastical sci-fi movie, Poor Things.

Ruffalo goes fully nude in the film, later rocking a series of spectacular suits meant to make him look birdlike for his portrayal of the egocentric, puffed-up, Duncan Wedderburn.

"Do you know I had an ass pad in? My legs were like four inches bigger. My calf was four [inches]. He really wanted the silhouette," Ruffalo reveals of his costume for the film, due out later this month. "I was wearing a corset with shoulder pads, so I was so squeezed in. It was even more extreme. He wanted me to look like a bird, so I had this whole built out chest piece that never made it because it was just too much. But the big ass pads, the leg pads, the thigh pads, the calf pads, those were all playing. So when you look at that and you're like, 'Wow, he looks great' -- now you know, I was just wearing what the Avengers wear, but underneath my clothes."

Touching again on their Avengers days, they each recalled the technobabble they had to learn for the films, something Downey called "absolute gobbledygook."

"You and I, the science bros, we would've these long passages about absolute gobbledygook," Downey Jr. shares.

"...bulls--t," Ruffalo quips.

While they admittedly didn't know the meaning behind what they were talking about, they knew it was important to their characters, so it was important to them.

"It'd be really hard to dig in," Downey Jr. recalls. "I mean, we would just drive each other insane on set going, 'Why can't I retain this? But again, we know when it's time to tighten things up a little bit.'

Speaking later on in the interview about the differences between filming on digital, as done with the Avengers saga, and on old school film, like Nolan did with Oppenheimer, Downey Jr. said he'd be happy to return to that sci-fi world that catapulted him to super stardom -- but not just yet.

"I will continue to love and I'm happy to eventually in some way reengage with sci-fi fantasy. It's got its own upside. But anything that over time takes you further and further away from the experience of just the hardware of what it is we do -- which is why it was also beautiful just to be shooting on film, not digital," Downey Jr. says. "I got used to digital after Zodiac, because I knew if Fincher's doing it, it's not going away. And is it more efficient? Yes. But you lose those natural rhythms of changing out the mag. It was just those little times everyone socialized."

Ruffalo asked Downey Jr. his thoughts on the future of film, particularly after making something like Oppenheimer, which while taking a more traditional approach to filmmaking was highly original.

"We have all of this product that is either already part of something or a brand. And then you have Oppenheimer come out, which is completely original source material. And it explodes in a time where people are really wondering, 'Well, what is cinema now after Marvel, after franchises, after IP?' What did you think about that?" Ruffalo asks.

"Honestly, I would be every bit as proud if it hadn't broken even or just done pretty good. But I think the great thing is it speaks to the audience's taste for novelty and for craftsmanship," Downey Jr. says of the film's massive success, which became the second-highest-grossing R-rated film in cinematic history following its release.

He adds, "Which is again why I'm telling you… I mean, Poor Things is already making a splash as it's on the horizon of coming out. You're next buddy. That's all I got to say."