In talking with Ruffalo they discussed what it is like inhabiting such an iconic character as Bruce Banner.
He's a guy struggling with two sides of himself - the dark and the light - and everything he does in his life is filtered through issues of control. I grew up on the Bill Bixby TV series, which I thought was a really nuanced and real human way to look at The Hulk. I like that the part has those qualities.
Another topic of discussion was Ruffalo picking up the role after Marvel and Edward Norton had a clandestine falling out.