Per an article on Comicbookresources:
Mark Ruffalo, the actor who plays Bruce Banner, aka the Hulk, has helped planned an three-movie arc for his character alongside Marvel Studios president Kevin Feige.
Though Marvel can’t produce a standalone movie for the Hulk due to tangled contractual rights, it hasn’t stopped the studio from utilizing the jade giant as a supporting character in other movies such as Avengers and Avengers: Age of Ultron. Now Ruffalo has revealed that Thor: Ragnarok is the beginning of an arc that’ll span over the next three movies he appears in.
Speaking with CinemaBlend, the actor explained how this wide-spanning story came to be. “Basically, Kevin [Feige] pulled me aside before [Thor: Ragnarok], and said, ‘If you were gonna do a… if we were going to do a standalone Hulk movie, what would it be?’ And I said, ‘I think it should be this, this, this, and this and this, and ends up like this.’ And he’s like, ‘I love that. Why don’t we do that in the next three movies, starting with Thor 3 and then we go into Avengers 3 and 4.’ And I was like, ‘That sounds great!’ And so we are at the beginning of this arc.”
Thor: Ragnarok loosely adapts the Planet Hulk storyline from Marvel Comics, which explains why the Avengers teammates run into each other so far off-planet, though it’s unknown where the character will go from there. We know he’ll be developing his ability to talk, thanks to a trailer for the Thor sequel, which Ruffalo explains is an important aspect of the character’s evolution.
“Hulk speaking is the start to separating of these two individuals, these identities in this split-identity person, and where that’s going to end up going. So it was really interesting to me,” the actor explained. “He’s like a baby! He’s like a five year old or six year old. So he has the same syntax, he has the same world view, and so it was fun. It’s like Chris [Hemsworth] – we all got to reinvent our characters in this.”