Avengers: Age of Ultron star Mark Ruffalo dishes out some interesting details about the nature of Hulk's role in the upcoming film.

Even though Bruce Banner looked pretty much in control of the green rage monster towards the end of The Avengers, the sequel will have him battle his alter ego - which wants to become the more dominant personality.

"There's a battle going on between these two opposing egos that live inside him," Ruffalo told Empire Magazine.

"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."

He says the rest of The Avengers prepared for this eventuality - which is probably why Tony Stark comes up with the Hulkbuster armour - but Ruffalo reveals that it was actually Banner who comes up with the "contingency plan."

The actor also mentions a scene in the sequel which will see the Hulk willingly transform back into Banner.

"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."

Talking about the possibility of a solo Hulk movie, the actor stated that he still has no clarity about it yet but he's definitely on board if they [Marvel] decide to make it.

"I can make The Hulk as real as any other character I've ever played and in ways more nuanced, more interesting. It's boundless," said Ruffalo. You can click here to read the full interview.