Learn more about the "Science Bros," Robert Downey Jr.'s Tony Stark and Mark Ruffalo's Bruce Banner in a new featurette for Avengers: Age of Ultron, in theaters May 1. Mark Ruffalo reveals that Tony and Bruce work very well together, while Robert Downey Jr. reveals why they created a "backup plan" in case Hulk gets out of control, the Hulkbuster armor.