Marvel cast Robert Downey Jr. as Iron Man after Fantastic Four audition

In the grand tradition of Marvel’s What If?, consider this: Instead of headlining 2008’s Iron Man, Marvel Studios’ first self-financed “Marvel Cinematic Universe” movie, Robert Downey Jr. secures his place in comic book movie history by taking on the role of Doctor Doom in 2005’s Fantastic Four. According to Jon Favreau, it could have happened.

In a new retrospective celebrating the 15th anniversary of Iron Man, Favreau — who not only directed the film but played Happy Hogan alongside Downey Jr. and throughout the MCU — sat down with Marvel Studios president Kevin Feige to look back at the movie that started the unstoppable entertainment machine. Favreau’s penchant for mixing comedy and drama, and the “latitude” he gave Downey Jr. when ad-libbing over the screenplay, wasn’t just a way of being “very consistent with Stan Lee’s tone,” as the director puts it, but the way Marvel broke out from the early 2000s Marvel movies and the grim tone of The Dark Knight, which would arrive later that year. Iron Man wasn’t just a movie it was a primordial soup.

“That tone you and Robert discovered on that movie became the template for what the MCU became,” Feige admits, with a look on his face that suggests it all could have gone very wrong. Casting Downey Jr. created his empire. “On later movies […] there were dark days,” the producer went on to say, “and I would say to Robert, ‘We wouldn’t be in this mess if it wasn’t for you.’ Meaning, we wouldn’t have a studio if it wasn’t for him.”

And as Favreau reminds Feige, it was possible Downey Jr. may have been out of contention for the role if Marvel, then spearheaded by Feige’s mentor Avi Arad, had plugged him into a different vehicle. The only reason Downey Jr. came in for a general read for the part of Tony Stark in Iron Man is because Marvel had already tested him for the role of Victor von Doom in Tim Story’s 2005 Fantastic Four, a role that eventually went to Nip/Tuck’s Julian McMahon. The bit of trivia kinda blows Feige back in his chair — Fantastic Four may not be a movie he fondly remembers. But it’s the butterfly effect moment that allowed the entire MCU to take shape.

Favreau pounds away at a simple fact throughout the entire 15-minute chat: Once he had his Tony Stark in Robert Downey Jr., everything else fell into place. Every decision was easier. Every actor globbed on. Every set piece, dramatic beat, and joke made sense. It was perfect casting. Feige does not hold back in taking his victory lap.

“That’s probably one of the greatest decisions in the history of Hollywood,” Feige says.