We still don't know much about how Doctor Doom (Robert Downey Jr.) will be introduced or the villain's motivations in Avengers: Doomsday, but several different sources have reported on the same details of the character's backstory.
Possible spoilers follow.
Apparently, Steve Rogers' (Chris Evans) decision to remain in Peggy Carter's timeline at the end of Avengers: Endgame caused a Multiversal incursion that resulted in the deaths of Victor Von Doom's wife and child. This leads to Doom seeking revenge on the former Captain America at the beginning of Doomsday (this may be teased in Endgame's re-release).
It sounds like a relatively simple and effective explanation for why Doom would target Rogers and his fellow heroes, but if a new rumor is to be believed, Marvel Studios had a few alternate scenarios in mind before the story fully came together - some of which were pretty out there!
Doomsday didn"Doom’s origin story in’t always involve him having a family," writes MTTSH. "Other versions included his parents dying, one where he believed he was a reincarnation of Tony and that he 'belonged' in the MCU, and one of the most insane ideas had him working for Mephisto, who was the real bad guy. Another version had him obsessed with either Pepper Potts or Sue Storm."
The scrapped Tony Stark reincarnation origin is arguably the most intriguing, since it would seem to indicate that the studio was considering introducing a more direct connection between Iron Man and Doom.
From what we've been told, Doomsday will not address the reason both characters look so similar, and Downey will only be seen without his mask once or twice when no other characters are around.
It's entirely possible that some of the potential plot points mentioned above could still find their way into this movie, Avengers: Secret Wars, or future MCU projects.
Avengers: Doomsday and Avengers: Secret Wars were hit with significant delays last year, with Doomsday now set to arrive in theaters on December 18, 2026, and Secret Wars positioned for December 17, 2027.
Both movies will be directed by the Russo brothers, who also make their MCU return after helming Captain America: The Winter Soldier, Captain America: Civil War, Avengers: Infinity War and Avengers: Endgame.
"Being able to create stories and explore characters within the Marvel Universe fulfilled a life-long dream of ours, and we discovered a powerful connection with audiences in each film that we made. We’re thrilled to collaborate once again with Kevin, Lou and the entire Marvel team to bring this epic adventure in storytelling to new and surprising places for both the fans and ourselves”, said The Russos in a statement after the SDCC panel.
Doomsday will star:
Paul Rudd as Ant-Man, Simu Liu as Shang-Chi, Tom Hiddleston as Loki, Lewis Pullman as Sentry, Florence Pugh as Yelena, Danny Ramirez as Falcon, Ian McKellen as Magneto, Sebastian Stan as Bucky, Winston Duke as M’Baku, Chris Hemsworth as Thor, Kelsey Grammer as Beast, James Marsden as Cyclops, Channing Tatum as Gambit, and Wyatt Russell as U.S. Agent
Along with Vanessa Kirby as Sue Storm, Rebecca Romijn as Mystique, Patrick Stewart as Professor X, Alan Cumming as Nightcrawler, Letitia Wright as Black Panther, Tenoch Huerta Mejia as Namor, Pedro Pascal as Reed Richards, Hannah John-Kamen as Ghost, Joseph Quinn as Johnny Storm, David Harbour as Red Guardian, Ebon Moss-Bachrach as The Thing, Anthony Mackie as Captain America, and, of course, Robert Downey Jr. as Doctor Doom.