A new MCU theory suggests that both Iron Man and Mister Fantastic will inspire Doctor Doom's plans in Avengers: Doomsday. Robert Downey Jr.'s return to the MCU, not as Tony Stark's Iron Man, but as Doctor Doom, is incredibly exciting, and while he has only been confirmed to be appearing in Doomsday and Secret Wars, there's speculation he could debut even sooner. The prospect of him appearing in a Marvel Studios movie this year and new comments from the returning directing duo, the Russo brothers, have spurred new theories regarding Doctor Doom's MCU debut.