Dr. Bruce Banner (Hulk) might have had a role in the creation of the supervillain Ultron while working alongside Tony Stark (Iron Man).
Actor Mark Ruffalo, who plays Hulk, hinted in an interview with Total Film Magazine that the two Marvel geniuses have been working closely together, resulting to "an experiment gone wrong."
"Banner's been living in Stark Tower," said Ruffalo. "He's doing work that augments Tony's own, which could lead to an experiment going wrong..."
He also said that Hulk will forger a deeper relationship with Scarlett Johansson's character, Black Widow because there's "something similar about the two of them." He called the two superheroes "lost souls."
Ruffalo also revealed that Banner's battle with "handling the hulk" continues in the film, and that it would be "much harder to come back from being Hulk than it is to get into him."
"The battle of identity going on between him and Banner is all about establishing dominance," said Ruffalo. "The only thing that Hulk is really afraid of is Banner."