A major MCU theory brings an incredibly dark twist to RDJ’s Doctor Doom, potentially explaining why the Marvel veteran was cast as the villain.

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.

MCU Theory: Doctor Doom’s Mind Takes Over Iron Man’s Dead Body

RDJ Returns As Tony Stark In A Way

There is a way for RDJ to return to the MCU as both Doctor Doom and Iron Man in one single role. According to a theory shared on Reddit by 0nlyHere4TheZipline, Doctor Doom’s mind could take over Iron Man’s dead body in an emergency. The theory hinges on the Fantastic Four reboot. According to a report, Robert Downey Jr.’s Doctor Doom is in The Fantastic Four: First Steps, making his debut in the movie’s mid/post-credits scene. The theory proposes that while RDJ’s Doom will appear in the credits scene, another actor will be playing Doom in the movie itself.

With Galactus as the Fantastic Four reboot villain and the team having to go to Earth-616, the theory claims Galactus devours the Fantastic Four’s Earth, with Doom forced to find a way to survive. The villain would then use a machine similar to the one he used to confront Mephisto in Marvel Comics, with his consciousness traveling the multiverse and landing on Tony Stark’s dead body, with Iron Man’s use of the Infinity Stones leaving a beacon for Doom. In the comics, Doom once transferred his consciousness into a dead Wolverine — though he transplanted his brain — which sets a precedent.

Marvel Studios Was Reportedly Considering To Resurrect RDJ’s Tony Stark

Marvel Has Been Looking Over Its Multiverse Saga Plans

The dark MCU theory for RDJ’s Doctor Doom connects to a past report about a possible Iron Man return. In November 2023, a report claimed that Marvel was considering a new Avengers movie with the original cast, meaning RDJ, Chris Evans, Chris Hemsworth, Mark Ruffalo, Jeremy Renner, and Scarlett Johansson would all return as their MCU heroes. Talks about the possible original Avengers reunion had started due to the MCU’s many issues in Phase 4, which stands as the franchise’s most criticized by far. The only problem with that idea is that two characters are dead.

However, according to the report, Marvel would resurrect RDJ’s Iron Man and Johansson’s Black Widow for the original Avengers’ reunion movie. At the time, it seemed like the report was talking about a traditional Avengers movie with the original crew back together; however, given Downey Jr.’s casting as Doctor Doom, it seems like that idea might have evolved into something else. RDJ’s Doom might not be the only twist to the original Avengers, with 2026’s Avengers: Doomsday possibly bringing back more of the original Avengers cast as different Marvel villains with a multiverse twist to them.

How RDJ As Doctor Doom Could Be The MCU’s Best Move

The Casting Injects Excitement Into The Franchise

RDJ’s casting as Doctor Doom has many fans excited about the future of the MCU, and for good reason. While a traditional Doom would have been great to see, having the MCU’s most beloved actor return to the franchise with a twist as perhaps Marvel Comics’ best villain is a fantastic alternative. After Jonathan Majors was fired from the MCU, Downey’s casting as Doctor Doom was the easiest way for Marvel to get audiences to forget about Kang the Conqueror, as the excitement about Downey’s return and the many questions around the casting took up the conversation.

Adding to that, RDJ’s recent Oscar win in an antagonist role, as well as his long career, show he has the acting skills to bring such a complex villain like Doctor Doom to life masterfully. Downey also has a past with the character, as the actor had talks to play Doctor Doom in the 2000s Fantastic Four movies before ultimately playing Iron Man in the MCU. Finally, RDJ being the face behind Doctor Doom‘s mask should lead to some heartbreaking moments as the Avengers discover the villain looks just like Tony Stark — or is him like the MCU theory suggests.