“In the film, Tony Stark (Robert Downey Jr.) becomes a friend to Banner, encouraging him to embrace the Hulk as a superpower instead of fearing the monster.
‘Tony’s the successful version of him,’ Ruffalo said. ‘He’s like a renegade scientist too, who used his own ideas on himself, but got everything that Banner hoped he would get. So yeah, I think he sees Stark as the successful version of himself, or what could be possible for him. Stark helps him come to the conclusion that maybe … having this enormous amount of energy and power can be used for something positive for once.’
Whedon said the relationship between Stark and Banner is ‘one of the most beautiful things in the movie. They bond over their intellectualism, but Tony is also from the start pushing him to stop being afraid,’ the filmmaker said. ‘And that’s not necessarily a smart idea, but it does turn into the right idea.’”
Ultimately, Ruffalo’s Banner finds himself at home, both in his Hulk alter ego and as part of the Avengers team. At the end of the film, Banner drives off into the sunset with Stark. Ruffalo said he has ‘no idea’ whether that relationship will carry over into ‘Iron Man 3,’ but that he would love to take on Bruce Banner again.