Ruffalo offers up where Bruce Banner is at when Avengers 2 begins:
I think he’s definitely matured a little bit since the last one. He’s become more acclimated to this thing and to being part of the team. I think he feels more a part of them all.
And on Hulk and Banner in Avengers 2:
Hulk is the kind of wild card. He’s the loose cannon of the group. He’s more like an atom bomb. You could guess where he’s going to go but he could go either way.
There’s a battle going on between these two opposing egos that live inside him. He’s definitely worried that the day is going to come when the Hulk gets the best of him, and maybe won’t release him, maybe won’t give him back. The Hulk knows this too. There’s a moment in here where he, begrudgingly, decides to go back to Banner. Who knows where these things will go, but as Bruce is able to impress his will on the Hulk, going into The Hulk and being inside the Hulk when he’s raging, The Hulk’s will is also growing and able to impress upon Bruce. That makes for some wild things. We’re laying the groundwork for that here. It’ll be interesting to see if that ends up being what would be the next Hulk movie.
About a potential Hulk movie:
Who knows, really? That’s such an amorphous thing. Nobody has talked to me about that yet. It seems people want it, but it’s tough. They’ve already done two of ‘em, and they’ve only done two Thors, they had a nice run on Iron Man. I feel like they have their plates full. There’s probably other people they’re keen on doing but I think people have shown that they’re ready to see another one.
"The Avengers: Age Of Ultron" hits May 1, 2015 directed by Joss Whedon starring Robert Downey Jr., Chris Evans, Chris Hemsworth, Scarlett Johansson, Mark Ruffalo, Jeremy Renner, Samuel L. Jackson, Elizabeth Olsen as Scarlet Witch, Aaron Taylor-Johnson as Quicksilver, Paul Bettany as Vision, with James Spader as Ultron.
When Tony Stark tries to jumpstart a dormant peacekeeping program, things go awry and Earth’s Mightiest Heroes, including Iron Man, Captain America, Thor, The Incredible Hulk, Black Widow and Hawkeye, are put to the ultimate test as the fate of the planet hangs in the balance. As the villainous Ultron emerges, it is up to The Avengers to stop him from enacting his terrible plans, and soon uneasy alliances and unexpected action pave the way for an epic and unique global adventure.
The Avengers 2 Trailer: