In the film, The Kids Are All Right star portrays genius scientist Dr. Bruce Banner, who transforms into the green beast when enraged.
But mellow, mild-mannered Ruffalo sheepishly admits he didn't struggle stepping into the role, confessing he once had terrible anger issues.
He tells the Associated Press, ""When I was a young actor, if you came to my apartment, you would have seen pictures and photos hung in the most bizarre places, where they were covering holes in the wall from auditions that I didn't get or slights that I felt I had suffered, where things were thrown, cups were thrown at the walls. I'm no stranger to that kind of anger and rage.""
However, Ruffalo, now a father of three, insists he's in a much better place.
He adds, ""But over time, I've, like a rock that's spent many times being tumbled around in the sea, I've sort of gotten the edges polished off of me. I'm not fighting the same fights that I was back then, the same demons.""