Marvel superstar Robert Downey Jr sparks new Avengers: Doomsday fan theory over possible dual role in the MCU movie, and I hope it's not true

• A new Marvel fan theory about Avengers: Doomsday is circulating online
• Fans think Robert Downey Jr is hinting that he'll play two characters in the MCU film
• A recent Instagram post from Downey Jr is to blame

Robert Downey Jr has sparked a new – and potentially huge – theory among Marvel fans about Avengers: Doomsday.

Last Saturday (July 26), the superstar actor, who'll portray Doctor Victor von Doom in the forthcoming movie, posted a seemingly innocuous video on Instagram.

For the most part, the footage shows Downey Jr hitting play on one of his son's (Indio Downey) songs on Spotify. Then, the A-lister briefly hovers his phone camera over a couple of Marvel comics, before turning it on himself to mouth along to the aforementioned tune.

It's those comics that have whipped Marvel Cinematic Universe (MCU) fans into a frenzy.

Well, one of them, anyway. The first comic we see is a copy of 'Marvel Super Heroes Secret Wars', aka the 12-issue run created by Jim Shooter, Mike Zeck, and Bob Layton that ran from May 1984 to April 1985. That's one of two 'Secret Wars' comic series – the second one coming from Jonathan Hickman and Esad Rebic from May 2015 to January 2016 – that Joe and Anthony Russo told me they're taking inspiration from for Doomsday and its sequel film Avengers: Secret Wars. The fact that Downey Jr is reading said comic series for research purposes, then, is no great surprise.

It's the other literary work, titled 'Iron Man: Legacy of Doom', that's sent MCU devotees into a tailspin, though.

Considering Downey Jr played Tony Stark and his superhero alter-ego Iron Man in the MCU between 2008 and 2019, some observers might think this is just a nod to the two iconic Marvel characters he'll have played by the time Avengers: Secret Wars arrives in December 2027.

However, long-time Marvel fans are reading much more into it and have even crafted a new fan theory about Downey Jr's casting in the Marvel Phase 6 film – a hypothesis that I most certainly hope is wrong. Potentially big spoilers immediately follow for the next two Avengers movies. Turn back now unless you really want to know what fans are theorizing about.

Is Robert Downey Jr playing two characters in Avengers: Doomsday?

For the uninitiated, 'Iron Man: Legacy of Doom' is a four-issue comic series that features another showdown between the eponymous armored superhero and Doom. Okay, the latter is more commonly associated as an archenemy of The Fantastic Four, but he's also engaged in a few tussles with Stark in Marvel Comics.

Indeed, 'Legacy of Doom' is he third time they lock horns on the page. The first came in a two-part Iron Man story called 'Doomquest', which landed on shelves in 1981, while the second occurred in 'The Doctor's Passion', another two-part narrative that was released in 1989.

Okay, but what's this got to do with Downey Jr possibly having a dual role in Avengers 5 and its sequel, which is already one of 2027's most anticipated new movies? Some fans believe Downey Jr is indicating that he's either playing Doom and an Iron Man variant, or confirms his Doom is a variant of Stark himself.

The latter is a theory that's circulated online ever since Downey Jr was revealed to be playing Doom in the MCU at San Diego Comic-Con 2024. Indeed, some fans have queried why Marvel would hire Downey Jr to play Doom if he wasn't an alternate universe's Stark who hadn't seen the errors of his ways like the MCU's Stark did, and who might have found a way to master dark magic and combine it with his self-developed technology. Hey, Ironheart already proved magic and tech can mix, so it's not as if someone like an evil Stark couldn't work out how to blend the two.

It's the other theory about Downey Jr potentially playing Doom and another version of Stark/Iron Man, though, that's got me worried.

If – and it's a big if – Doomsday adapts some aspect of 'Iron Man: Legacy of Doom', we could have a situation where the aforementioned situation becomes reality. If it does, we could see Downey Jr's Doom and a Stark variant, who'd also be portrayed by the A-lister, fight it out to show how powerful Doom is and/or if Doom needs to acquire some tech that Stark has perfected.

The other possibility is that Downey Jr will reprise his role as Stark/Iron Man in Secret Wars. There have been murmurings that Chris Evans may return as Steve Rogers/Captain America in the sixth Avengers movie, which is reportedly being billed as a celebration of every Marvel comic book universe to ever exist before the MCU undergoes its soft reboot post-Secret Wars. That includes 20th Century Fox's X-Men franchises, Sony's three Spider-Man universes, and the MCU.

Should that prove to be the case, in Marvel's eyes, it wouldn't be a fitting commemoration without Downey Jr's Stark being a part of it. After all, he kickstarted the comic giant's cinematic universe.

Nevertheless, bringing back Downey Jr as Stark in any form would undo his heart-breaking yet heroic sacrifice in 2019's Avengers: Endgame. In my view, that was the fitting albeit bittersweet farewell that he deserved, and I'd be loathe to see him return as Iron Man in Doomsday and/or Secret Wars because of it. This is one fan theory, then, that I don't want to see materialize.

Avengers: Doomsday will be released in theaters on December 18, 2026.

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