It was a reveal that changed the Marvel Cinematic Universe – and riled up nerds.

When Robert Downey Jr. ripped off a Doctor Doom mask at Comic-Con and the erstwhile Tony Stark announced himself to be the MCU’s next iconic big bad, the atmosphere in the room was electric. Fans leaped out of their seats to cheer. Reporters scrambled to record the moment on their phones (or type furiously on a live blog). And Downey smirked at "Avengers" directors/collaborators Joe and Anthony Russo and Marvel's head honcho Kevin Feige, eating up the attention not unlike, well, a comic-book megalomaniac.

The internet memes came fast and furious: There were various images passed around from "Oppenheimer" – a nod to Downey's co-star Cillian Murphy being a fan favorite to play Victor Von Doom – and Daniel Craig’s “Knives Out” detective saying, “It’s just so dumb.” Everybody was talking about the beloved A-lister's return, and much of the chatter leaned negative.

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But this is Downey! Deadpool might call himself “Marvel Jesus,” but come on, we all know who the real MCU messiah is. A whole universe was built around Downey's superhero introduction in 2008’s “Iron Man.” He went out like a champ in “Avengers: Endgame,” with a heartfelt goodbye, and his presence is still felt throughout the Marvel movies.

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His Doom heel turn is both inspired casting and the safest decision Marvel has ever made. It pulls the MCU out of a rut, where even its most ardent supporters have wondered what’s going on, and together with the runaway success of "Deadpool & Wolverine" is a needed adrenaline shot. The move also sets up an unfortunate precedent, focusing on veterans rather than raising a fresh crop of faces who could be the franchise's future. How many times can they pull the “Pay Downey if emergency” alarm?

He wasn’t exactly Plan A here. The MCU enjoyed several years of beloved fandom and unstoppable box-office hits. However, the post-“Endgame” movies and TV shows, with new characters, alternate-world variants and shenanigans involving time and space, have been a mixed bag. The Marvel universe had been this intricately crafted, intertwined storyline – now heroes are off on their own missions and nothing is substantially connected, not like it had been. And don't forget Jonathan Majors, who was introduced to be Kang the Conqueror and has since been ousted after legal issues.

So “Avengers: The Kang Dynasty” becomes “Avengers: Doomsday,” the Russos sign on for that and “Avengers: Secret Wars,” and instead of recasting Kang, Downey gets a Brink's truck of cash and his grand return as a villain. Rather than new stuff, Marvel is playing the hits. 

While MCU critics break out the knives every time Feige sneezes, they do have a point in that Hugh Jackman, Chris Evans and now Downey have all come back after having poignant farewells. Yet this is perhaps the most comic bookish thing Marvel has done. For decades on the page, superheroes have died and been reintroduced, often coming with a creative refresh; Disney’s just doing it onscreen with an Oscar winner instead of with Steve Rogers.

Also, apologies to Kang, Ultron and even Thanos, but there’s no bigger Marvel Comics baddie than Doctor Doom. It’s why folks are in such a snit about Downey, as he could have been any number of high-profile actors. Sure, Murphy could kill that role, but there’s an interesting symmetry to have the man behind the Iron Man mask now take on Doom’s.

“I like playing complicated characters,” Downey said at Comic-Con, with massive understatement. And who’s to say this Doom isn't an evil Stark variant, or he’s a Doom but not the Doom – Marvel has played with fan expectation before, and it’s canon that character variants don’t have to look like one another (for example, John Krasinski played Reed Richards in the “Doctor Strange” sequel and Pedro Pascal is the hero in “The Fantastic Four: First Steps”).

What hopefully, this doesn’t mean is that Marvel’s done with its big swings and everything’s going to be, as Deadpool quips in his new movie about Evans’ return, “the superhero equivalent of comfort food.” The MCU became special when it took risks on more obscure characters (like Ant-Man and Guardians of the Galaxy) that paid off and let directors with vision and voice, such as James Gunn and Ryan Coogler, cook.

The next movie up, “Captain America: Brave New World,” weaves together different takes on the familiar: Anthony Mackie’s Sam Wilson as Cap, a “Winter Soldier”-esque vibe and Harrison Ford hulking out. But for those yearning for the new, “Fantastic Four” (now in production) seems like a different, retro-cool adventure that will move the MCU forward rather than back. 

Swapping major names seems to work in politics and we’ll see how that fares with comic book movies. Downey chewing scenery behind a mask for a couple of movies sounds delicious but, however tasty, even leftovers start getting old. Figure out the multiverse mess, let “Secret Wars” wrap all that up, and pave the way for the “Avengers vs. X-Men” movie that everybody's dying to see and all will be well.

Just please don’t cast Downey as Professor X.

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