A new Marvel Cinematic Universe theory offers a great possible explanation for why Robert Downey Jr. was cast to play Doctor Doom. Downey is the most important actor in the MCU, having started the franchise with 2008’s Iron Man. The announcement that he was returning to Marvel Studios for the first time since 2019’s Avengers: Endgame would have been shocking in itself, but the fact that he will be playing Doctor Doom, not Iron Man, in multiple upcoming MCU movies made the return even more surprising. Marvel did not explain how RDJ could play Doctor Doom.

Downey became popular in the MCU for giving life to Tony Stark. After Iron Man’s sacrifice in Avengers: Endgame, it seemed like Downey had moved on from Marvel, pursuing different kinds of films, which led to the star winning Best Supporting Actor for Oppenheimer at the Oscars and many more awards. With the multiverse, anything is possible, so Downey’s Doctor Doom might not come from Earth-616, the same as his Iron Man, but another universe. However, a dark MCU theory offers a more complex twist to the reason RDJ was cast as Doom, setting up Avengers: Doomsday’s story.