Robert Downey Jr. thinks Mark Ruffalo's "a little insane".
Mark Ruffalo
The 'Avengers: Age of Ultron' star - who plays The Hulk in the Marvel flick - says his co-star has the "most endearing" patience for him and his crazy antics.
He said: "He's been just a bro to me. He also thinks I'm a little insane. So when we get into those moments, we are half laughing through the whole thing. He's half like, 'Ruffalo, how do you even get up out of bed?'
"He has the most endearing sort of patience and tolerance for me. And we literally are laughing behind everything. I don't know what's going to come up with him, which makes it so much fun and alive.
"We also know that we're playing on this theme of the science bros that's so wildly loved. And so we're playing that up. You sort of understand that whole phenomenon. He's like a brother to me."
The 47-year-old actor also revealed Robert, 50 - who stars as Iron Man in the film franchise - helped him overcome the "doubts" he had whilst playing the comic book character.
He added to PEOPLE magazine: "He's kind of my godfather in the world. He sort of gave me the okay to come join and has sort of bolstered me along the way when I've had my doubts, which are plenty. And he has made sure that Banner's been well represented."
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