All of the Marvel Studios productions up to and including The Avengers can be grouped together and dubbed the introductory phase. Phase 2 sends the heroes we met on new adventures as established, more confident and experienced characters before they come back together in The Avengers: Age of Ultron. After that it’s still a mystery but all signs point to Phase 3 (beginning with Ant-Man in July 2015) of the Marvel Cinematic Universe introducing quite a few new heroes, leading to an inevitable rotation of The Avengers roster.

There have been rumors ever since The Avengers broke box office records around the world that the popularity of Ruffalo’s character – both as Bruce Banner and in performing the motion capture for the Hulk – could lead to the character getting another solo feature. Ang Lee’s Hulk and Louis Leterrier’s The Incredible Hulk didn’t make the needed money to justify a followup on Marvel’s two-films-per-year schedule, leading us to believe the Hulk may be better served as a supporting character or partner in a team-up, but Marvel Studios boss Kevin Feige did tease his interest in the Planet Hulk and World War Hulk stories from the comics and Ruffalo has some ideas of his own.

While appearing at the Sundance Film Festival this weekend for Infinitely Polar Bear, Mark Ruffalo spoke on a topic very close to him – protecting and maintaining the environment. He explained that artists like him who can reach large audiences have a responsibility to share the positives of science in that respect, without being extreme. During the Q&A he was asked about how he’d like to do that with large blockbusters like his role as Hulk in The Avengers.

“I think that’s the way to go, and it’s a trend that’ll start to develop. As a culture, when we latch onto a fad, we’re actually working something out in the creative subconscious. The fact that all these doomsday and end-of-times movies are coming out is because we’re actually working that out in the culture.”

“I’m in The Avengers, but if you took my screen time 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.”

Ruffalo did sign a multi-picture deal with Marvel that lets the studio call upon him for another four appearances after The Avengers: Age of Ultron. Whether or not a Hulk standalone picture is in the cards we don’t yet know but we wouldn’t expect it until possibly Phase 4 (after The Avengers 3) – That is, unless Marvel surprises everyone and sneaks it into one of their 2016 or 2017 release dates. Perhaps the end of Age of Ultron could set in motion the events leading into another Hulk adventure. How that could involve the environment outside of Hulk smashing stuff in it is anyone’s guess.

MTV caught up with Ruffalo at Sundance as well and asked him for some quick thoughts on The Avengers 2 script that was just recently sent out to the cast by Joss Whedon.

“I would say that it’s better, it’s cooler, it’s more awesomer. It’s a little bit darker, but also really has Joss Whedon’s incredibly, witty and sly sense of humor.”

It’s a brief tease but Ruffalo’s words echo that of Scarlett Johansson who described it as “dark” and “cerebral.” Should Marvel give Hulk another solo feature before The Avengers 3 or would you rather the studio take that slot to introduce a new character? Share your thoughts in the comments!

More: Marvel Boss Talks ‘Avengers 2′ Title & Roster

Captain America: The Winter Soldier hits theaters on April 4, 2014, Guardians of the Galaxy on August 1, 2014The Avengers: Age of Ultron on May 1, 2015, Ant-Man on July 31, 2015, and unannounced films for May 6 2016, July 8 2016 and May 5 2017.

Follow Rob on Twitter @rob_keyes for your Marvel movie news!

Sources: MTV, Total Film