Who is Doctor Doom? Robert Downey Jr.'s shocking Marvel casting explained

Like Thanos himself, Robert Downey Jr.'s return to the Marvel Cinematic Universe may have been inevitable. But few expected it would go down like this.

On Saturday, Marvel revealed at the pop-culture convention Comic-Con that Downey is coming back to the franchise in the upcoming movie "Avengers: Doomsday" (2026), which will be followed by "Avengers: Secret Wars" (2027). But rather than reviving Tony Stark/Iron Man, he's taking on a new role as one of Marvel's most iconic villains: Doctor Doom.

So who is Doctor Doom (aka Victor Von Doom), and why is it so significant that Downey is playing him?

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Is Robert Downey Jr. coming back to Marvel? What to know about Doctor Doom, his character in the new 'Avengers' movie

Introduced in a 1962 issue of "The Fantastic Four," Victor Von Doom is a genius scientist originally from Latveria, a fictional European country. The infamous supervillain is also the adversary of the Fantastic Four's Reed Richards, whom he met when they were both students. Pedro Pascal has been cast as Reed Richards, aka Mr. Fantastic, and will debut as the character in 2025's "The Fantastic Four: First Steps."

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In the comics, Von Doom is scarred after a machine he invents explodes, leading him to wear a mask and suit of armor. He later becomes monarch of Latveria and seeks world domination. Doom "craves power, control, and acknowledgement that he's the best at everything," according to Marvel.com. "Whether he's using time travel, making deals with demons, or even teaming with his enemies to fight a common foe, Doom's endgame is to be the one in charge." He also uses magical spells.

Doctor Doom has been played onscreen by Julian McMahon in the 2005 "Fantastic Four" movie and Toby Kebbell in the 2015 reboot. The character also had a key role in Marvel's 2015 "Secret Wars" comic and creates Battleworld, a planet where various universes collide. This story could serve as inspiration for the movie "Avengers: Secret Wars."

Will Robert Downey Jr.'s Doctor Doom be connected to Iron Man?

Ever since Marvel announced a new "Fantastic Four" movie, Doctor Doom has been expected to come to the MCU. But the idea that the studio would cast the same actor who played Iron Man, one of its most beloved heroes, as the iconic villain was a shocker. How this will work hasn't been made clear.

But "The Fantastic Four: First Steps" takes place in an alternate universe, so Downey's Doctor Doom likely originates from there and not the main MCU timeline. This could mean that the actor's rendition of Doom will actually be an evil, alternate version of Tony Stark.

Or Doctor Doom may happen to look like Tony Stark but be otherwise unrelated to him. If Doom is always hidden behind his mask, Downey could also be disguised to the point that it isn't obvious that it's even him. At Comic-Con, "Avengers" directors Joe and Anthony Russo confirmed simply that their Doctor Doom is still named Victor Von Doom.

The casting was a surprise because many fans expected Downey would reprise a heroic version of Iron Man from an alternate universe in "Avengers: Secret Wars." Given there are infinite universes to pull characters from, that could theoretically still happen on top of the actor's Doom role.

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Casting Downey as Doom represented a pivot for Marvel, which at Comic-Con in 2022 announced that its next "Avengers" films would be titled "Avengers: The Kang Dynasty" and "Avengers: Secret Wars." The former would focus on Jonathan Majors' Kang the Conqueror, a villain featured in "Ant-Man and the Wasp: Quantumania."

But "Quantumania" underperformed at the box office last year, and Marvel dropped Majors after he was found guilty of assaulting his ex-girlfriend. The renaming of the next "Avengers" movie from "The Kang Dynasty" to "Doomsday" suggests Marvel is pivoting away from Kang to make Doom its next big bad.

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Fans have mixed feelings about Robert Downey Jr.'s casting, with some suggesting Mads Mikkelsen should have played Doom

The reaction to the bombshell casting news has been mixed, with some fans saying they wished a new actor had been given a chance to play Doom. Others expressed trepidation at the idea that the casting could lead to changes to Doom's backstory, assuming he is a Stark variant.

"RDJ is great, but I sorta hate this casting and if they completely change Victor Von Doom yet again (I'm) going to be disappointed at best," one fan commented on Reddit.

"I just … I don't know … I want the real Dr. Victor Von Doom before I get some stunt variant," writer Adam Frazier posted on X, while writer William Bibbiani said, "Doctor Doom is one of my favorite characters in comic book history and I am genuinely disappointed that he's being sold to us as 'Evil Iron Man' instead of his own, distinct character."

Other fans suggested Mads Mikkelsen, who previously played the villain Kaecilius in "Doctor Strange," would be a better fit as Doom. "If we're bringing back MCU actors … MADS IS RIGHT THERE," one fan commented on Reddit.

All in all, it may be the biggest risk Marvel has taken in years. We'll find out if it pays off when "Avengers: Doomsday" hits theaters in May 2026.