The actor, who took on the role previously played by Edward Norton, described The Hulk as "mercurial".
"He's very unpredictable; he's nuanced," Ruffalo told Flicks and Bits. "There's a sense of humour there, there's an ability to communicate.
"But he's bristly and he's incredibly dangerous - like a wild animal. His rage feels real, his reactions to things feel human."
Ruffalo went on to explain that both writer-director Joss Whedon and he had felt that it was important to give the character a sense of humour in order to humanise him.
"What appealed to both Joss Whedon and I about the character is that he would have a common man sort of feel to him and possess this world-weary charm. We agreed he should have a sense of humour about his situation," he said.
"Based on the last incarnation of The Incredible Hulk, there was the promise that Bruce Banner may actually have a little control over the behemoth. We wanted him to be fun and interesting as Banner and awesome as The Hulk."
unsure about the possibility of a solo Hulk movie.
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Watch Ruffalo discuss playing The Hulk below: