Avengers: Infinity War represents the culmination of the Marvel Cinematic Universe to date, going all the way back to 2008's Iron Man. That movie saw Robert Downey Jr. assume the role of Tony Stark--Iron Man--in one of those truly perfect actor-character pairings. Whether it's in Infinity War or further down the line, he'll eventually move on from the character, but those will be impossible shoes to fill, in the mind of Joe Russo.
The Infinity War co-director told The Hindu Times (via ComicBook.com), "There is nobody who can take over Iron Man from Robert. I don't think the audience would accept that. He never mentioned to us about leaving Iron Man, but it will happen at some point of time."
With Thanos finally showing up in a meaningful way, it seems likely that characters will die. We've already made predictions about who will live and die, and Iron Man feels like a strong candidate to fall into the latter camp.
"He can't play the character forever," Russo continued. "I am sure there are lots other things he wants to do in his career. But he loves playing the character, I know that, and we love working together. We will see where it goes from here."
Russo's comments certainly sound as if Iron Man is safe in Infinity War, although that might be intended to throw fans off. The same could be said for talk about Captain America actor Chris Evans leaving after Avengers 4 next year, rather than following Infinity War (which releases on April 27).
Iron Man has been perhaps the most prominent character in the MCU, showing up in numerous films, including last year's Spider-Man: Homecoming. Some fans have speculated that the breakout character from Black Panther, Shuri, could assume the role of Iron Man, much as the new comic iteration of Iron Man is a young woman.
The 53-year-old Downey, for his part, has said before that he hopes to retire from the role "before it's embarrassing." Aside from being one of the most beloved MCU characters with fans, Downey has also proven popular with his co-stars--especially with Chris Pratt.
Info from Gamespot.com