Mark Ruffalo based his performance in 'Marvel Avengers Assemble' on gorillas.

The 'Kids Are All Right' actor portrays Bruce Banner/The Hulk in the forthcoming film, and he admits he watched videos of the great apes so he could mimic their lumbering quality.

He said: ''Believe it or not, I looked at a lot of gorillas, and just because they have this kind of lumbering to them that then becomes explosive. I liked that. He doesn't move quickly; he has this kind of lumbering thing, and his shoulders are a little rolled over, you know.''

Mark was initially worried he would only be an extra character in the film, which also stars Robert Downey Jr. (Iron Man), Chris Hemsworth (Thor) and Chris Evans (Captain America), and made sure to check with the director Joss Whedon before he signed up.

He added to ''It's hard to have this many characters, this many storylines, and have each character start to make an arc. That was my worry - I said, 'Joss, don't put me in there if I'm just going to be standing around. There's no reason to'.

He's like, 'No, no, no, don't worry - everyone's gonna have their voice, and their sort of own little character arc.' And he's really come through on that. He was kind of enough to give me a couple of scenes, where he was heading - and we worked a lot together on The Script.''