The Marvel Cinematic Universe may just be another blockbuster franchise at its core, but one thing it’s done a decent job with is picking its talent. Granted, not every casting decision has been a slam dunk (sorry, Mickey Rourke), but Marvel Studios managed to recruit a lot of big names over the years, from Anthony Hopkins playing Odin in the Thor movies to Tilda Swinton playing The Ancient One next year in Doctor Strange. However, if you ask Nick Fury himself, Samuel L. Jackson, he’ll tell you that the success of this franchise has more to do with the characters and genre rather than the actors.
During THR’s Actors Roundtable, Jackson was asked if he felt "personal validation" because his superhero films have been so popular. This was his response:
Those movies have very little to do with us. They have to do with the event. People love superheroes, and fortunately we’re in them, but they’re not dependent upon us. They could put that eye patch on somebody else, and it would work the same way. The green guy could be anybody. You turn Terrence Howard to Don Cheadle and nobody notices.
Funny enough, the MCU itself hasn’t seen that many casting changes. The only major ones have been Don Cheadle taking over War Machine from Terrence Howard, Mark Ruffalo inheriting The Hulk from Edward Norton, and Zachary Levi taking Josh Dallas’ place as Fandral (though that one was barely noticeable). Still, Jackson does bring up a good point. Marvel’s characters have existed on the printed page for decades, to the point that most kids know who Spider-Man and Captain America are before they’ve heard of the actors who play them. These properties are so popular that the movies haul in cash even if a new face is brought aboard to replace someone else, though obviously something as extreme as an entire cast overhaul would raise eyebrows.
However, in Jackson’s case, he’s not even remotely close to being replaceable in this franchise. First off, his Nick Fury is based off the Ultimate incarnation, who was purposefully redesigned early on to look like Jackson in the first place. Beyond the identical resemblance, Jackson has also been part of the franchise since the beginning, being the key connective thread in Phase One. We know Jackson won’t reprise his role next year in Captain America: Civil War, but with two movies left on his contract, no doubt we’ll either see him pop up in the Avengers: Infinity War movies or one of the other entries in either Phase Three or Four.
Now that the MCU is almost 10-years-old, it will be harder to recast certain characters, though for new series like Doctor Strange, Black Panther, and Captain Marvel, it will be easier since they’re not as established. Obviously certain disagreements and issues are unavoidable, but when in doubt, it’s best to maintain continuity regarding appearance.