Robert Downey Jr’s latest tease about Avengers: Doomsday and his impending appearance in the movie as Doctor Doom makes a major MCU movie theory seem even more likely for the film. While more than one MCU actor has played multiple roles in the franchise thus far, Robert Downey Jr. returning as Doctor Doom is perhaps the biggest and most important example of this concept that we’ve seen to date.
Avengers: Doomsday will effectively take Robert Downey Jr. from being the biggest hero in the MCU timeline, to being its biggest villain – which is a major matter to say the least. That said, the way in which this return is being teased suggests the actor’s story as Iron Man may be more linked to Doom’s rise than it could otherwise appear.
Robert Downey Jr’s Thanksgiving Marvel Post Makes One Avengers: Doomsday Theory Seem Look Even More Likely

tony stark trying out his iron man gauntlet in the mcu
November 27 saw Robert Downey Jr. post to social media with an image featuring Doctor Doom and Iron Man, showing the pair’s hands as they break a wishbone between them. Based on the post’s proximity to Thanksgiving, it seems this is intended to tie in to the holiday, wherein breaking a wishbone is a tradition intended to give good luck to whoever gets the larger piece.
Robert Downey Jr’s various updates and posts alluding to his role playing Doctor Doom in Avengers: Doomsday are interesting first and foremost in their content, but also in the sense that his prior role as Iron Man seems to be brought into the conversation as much as possible, as is the idea of Tony Stark and Victor Von Doom having a shared history in the pages of Marvel’s comics.
Of course, this makes sense given the actor is playing both roles in the MCU, but the insistence on tying Doctor Doom back to Tony Stark in the build up to Avengers: Doomsday certainly supports the theory that Doctor Doom’s story in the franchise will be linked back to Iron Man in some major way.
While efforts have been made to underscore that Robert Downey Jr. will be playing Victor Von Doom in Avengers: Doomsday and not a different Tony Stark, this doesn’t prevent the story from either revealing that Iron Man and Doctor Doom’s multiversal fates are intertwined or connected in some way, or revealing that an alternate universe Iron Man plays a key part in Doctor Doom’s story.
Connecting Robert Downey Jr’s Iron Man & Doctor Doom Is The Only Real Way To Avoid Several MCU Issues

Tony Stark stands next to one of his suits in Iron Man 3
Ultimately, giving Robert Downey Jr’s Doctor Doom some tangible in-universe connection to Iron Man – be that the iteration the actor previously played, or otherwise a different variant – makes sense in terms of helping justify Downey Jr’s return on a narrative level.
Currently, a lot of the criticisms and concerns around the major MCU actor returning in a new role revolve around the idea that Robert Downey Jr’s return is nothing more than an attempt to reignite fan investment in the franchise following Iron Man’s death in Avengers: Endgame without building new stars or paths forward for the MCU.
Providing an in-universe story reason the casting had to be Robert Downey Jr. would negate these criticisms, while also helping provide connective tissue for the overarching universe and the next chapter of the MCU – which means there’s plenty of reason to hope the teases of a link between Doctor Doom and Iron Man’s stories come to fruition, be that in Avengers: Doomsday or later.