He's returning as The Hulk in Joss Whedon's Avengers: Age of Ultron next year, but Mark Ruffalo says that if Marvel makes a new standalone Hulk movie, he would like it to include an eco-friendly message.
Talking to Total Film, he said that "as artists we have an ability to reach a lot of people in a deep way, and we have a responsibility. What we have to do as storytellers is to take science and make it relatable. I think we have to tell the story of the positive and what we're going to try to do. Give them alternatives but don't make it a polemic."
He added: "I'm in The Avengers, but if you took my screentime it would come to about ten minutes, along with the 12 other people I'm sharing the screen with, so my input's kind of limited on that. But if we get to a standalone Hulk movie, I'll have a much better chance to do that. I'm just learning now how to find my voice and bring it into the studio world."
Avengers: Age of Ultron hits theaters on May 1, 2015.