To say that the Marvel Cinematic Universe is a great and industry-altering project is not exactly an original thought these days. It's also not a false one. Despite having their first out and out flop in Netflix's Iron Fist, the Marvel machine shows absolutely no sign of slowing down and all upcoming films look to be great works. One of the keys to the MCU's success has been it's stellar casting. From the genius decision to cast an actor looking for a comeback as a narcissistic in a suit of armor to turning a relatively unknown Australian beefcake into a brooding God of Thunder, the Marvel casting agents have never failed to find the most suitable actor for each and every role.

RELATED: 15 Reasons We Need Death In The MCU

However, after nine years, 16 films, and a handful of TV shows, several actors in the MCU have expressed a desire to move on to other projects. In addition, it might make narrative sense for a few characters to be renovated for the sake of the story, meaning that the actors involved would need to be replaced. It's an unfortunate truth that many of the MCU icons will leave the silver screen eventually, but it's also a fun thought experiment to wonder who could replace them.

15 CAPTAIN AMERICA

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It's almost a guarantee that Steve Rogers will bite the dust in the next Avengers movie. His death would bring a logical conclusion to several story arcs, it would line up with his many deaths in the comics, and actor Chris Evans has been very public about wanting to continue with more serious work. Therefore, the question is not so much if he'll be replaced but rather when. After all, you can't have the MCU without Captain America. You just can't.

Logical choices seem to boil down to either Anthony Mackie's Sam Wilson or Sebastian Stan's Bucky Barnes, but Barnes's self-imposed cryogenic coma at the end of Captain America: Civil War made it clear that lifting the iconic shield himself would bring his character full circle in a satisfying conclusion.

14 HAWKEYE

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When Jeremy Renner's Clint Barton revealed his secret family in the second act of Avengers: Age of Ultron, it was almost assumed that he would die later in the movie as an emotional payoff. That didn't happen of course, and we last saw him in the Raft prison in Civil War where Tony even asks him why he abandoned his family. Knowing Clint has people who love and rely on him suddenly makes his precarious vocation uncomfortable to watch.

Every bullet fired at him becomes all the more frightening when faced with the prospect of the visual of his mourning family. Though clearly he will be returning to resolve his issues with Iron Man, it may soon be time for Hawkeye to retire permanently, perhaps passing his down bow to Kate Bishop who could be played by any number of talented young actresses.

13 ANT-MAN

Ant-Man

In a perfect world, Paul Rudd would play all characters in every movie forever. The man is a legitimate treasure of the screen and has never failed to inject humor and enjoyment into any role he's played. Unfortunately, a plot line in his debut film in the MCU made it clear his time in the suit is limited.

Michael Douglas's Hank Pym openly states that his shrinking suit damages its user's body over time, thus the reason he needed to find Rudd's Scott Lang in the first place. Knowing that his body will eventually reject the suit, the logical decision is to find him a replacement. One already exists in the comics in the form of the irredeemable Eric O'Grady, whose explicit antics could provide the MCU with it's first foray into the lucrative field of R-rated films.

12 IRON MAN

iron man

Robert Downey Jr. was the perfect Tony Stark and has played the character in eight films. He's still a cornerstone of the MCU and a major box office draw, but the fact of the matter is that the man is getting old. Though he looks half his age, RDJ is 52 and his central character arc has already come to a close, which means it's probably a good time to switch things up when it comes to Iron Man.

The once carefree playboy has morphed into a loyal but compassionate adult capable of mentoring a young hero and dealing with his personal demons. As fun as Downey still is, there's nothing more to learn about his character and it may be time to give either Don Cheadle's Rhodey or Riri Williams a turn in the main armor.

11 JANE FOSTER

Jane Foster Natalie Portman

The trailer for Thor: Ragnarok made two things abundantly clear: the movie was going to be awesome and Natalie Portman's Jane Foster would not be returning in any capacity. The female lead would be Tessa Thompson's Valkyrie. Portman and Marvel Studios have not officially called it quits, but seem to be taking a professional break with each other.

There doesn't seem to be any plans in place to bring Jane back, but Portman has already filled her slate with other films meaning if they do want to return to the character, Portman will likely be unavailable. With Rachael McAdams and Benedict Cumberbatch raising the bar on Marvel romances, this may be an opportunity for Marvel to recast the role with an actress who can have more onscreen chemistry with Chris Hemsworth.

10 STARHAWK

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Sylvester Stallone showed up as this minor character in Guardians of the Galaxy Vol. 2 to chastise Michael Rooker's Yondu for breaking the Ravager Code and to provide a beautiful and cathartic ending to the film. He sounded bored, barely acted, and it felt like he was phoning his minor performance in.

With one of the many mid-credit scenes suggesting he may return along with his team of the original comic versions of the Guardians of the Galaxy, including Ving Rhames as Charlie 27, Michelle Yeoh as Aleta Ogord, Michael Rosenbaum as Martinex, and Miley Cyrus (yes really) as Mainframe. If they do return, then it would be prudent to replace Stallone with an equally intimidating actor, albeit one that actually looks like he wants to be there.

9 IRON FIST

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Iron Fist is the first and so far only surefire failure in the MCU. The plot, action, cinematography, dialogue, character development, and casting were all tasteless at best and offensive to fans at worst. Even Rosario Dawson returning as fan favorite Claire Temple couldn't breath life into this series. And the worst offender of all was Finn Jones as the eponymous alter ego of Iron Fist, Danny Rand.

Playing a white character blatantly appropriating Asian culture would have been hard enough to make likeable, but Jones being as bland and obnoxious as he possibly can be certainly doesn't help. Most recastings require some sort of explanation on the part of the show, but Finn Jones could be switched out halfway through the upcoming Defenders series and nobody would complain or question it.

8 NICK FURY

Nick Fury

It feels almost sinful to suggest the man who organized the MCU based on a single, 30-second cameo in Iron Man should be recast. After all, the role was quite literally written for Samuel L. Jackson and he plays it with the suave confidence that comes from knowing that he couldn't play it wrong even if he tried. Nick Fury is a spy among spies, the best secret agent in the Marvel world. As Tony Stark put it, "His secrets have secrets."

It would not be out of character for him to hire a devoted body double to serve as his public face while the real Nick Fury operated out of a secret bunker. Besides, David Hasselhoff has claimed his version of Nick Fury was better in the 1998 TV-movie Nick Fury: Agent of S.H.I.E.L.D, so why not give him a chance to prove it?

7 LOKI

Loki

The breakout star of the first Avengers movie, Tom Hiddleston established Loki as a pop culture icon by playing the character to perfection. His fate in Thor: Ragnarok is as yet unknown, but it would be remiss for Marvel Studios to ignore a popular part of Loki's comic book lore. Loki has appeared as a child in the form of Kid Loki, a reinvention of his character which gave Thor an opportunity to be the brother he always strove to emulate.

Kid Loki was a hero for a time, thriving under Thor's influence, but he eventually reverted to his former, villainous ways. Not only would introducing Kid Loki to the MCU provide an opportunity to showcase deserving young talent, but the tragic tale of Thor trying and failing to save his brother's soul would be a compelling story arc to even non-comic book readers.

6 HULK

The Hulk being hit by lasers

Bruce Banner has already been recast in the MCU, trading hands from Edward Norton to Mark Ruffalo who's successfully played the part since. Though his involvement in Thor: Ragnarok has been hyped up, the whole reason Thor will encounter Hulk in the Grandmaster's arena is because he's trying to escape his pariah status on earth.

After going on an unintentional rampage in Avengers: Age of Ultron, it makes sense for Banner to be hesitant to return to earth, which will leave a giant, Hulk-shaped hole in the Avengers' roster. Could William Hurt's return as 'Thunderbolt' Ross in Civil War be hinting at the Red Hulk coming to the MCU? Could we potentially see Amadeus Cho enter the scene? Is there a chance we might see She-Hulk? Please?

5 ELEKTRA

Elektra from Netflix Daredevil

Daredevil was the risky MCU experiment to see if their cinematic formula could work as a limited Netflix series. It paid off in dividends with a popular and flashy story that gave the streaming service its own private corner of the MCU. Daredevil's second season offered more of what people loved, and introduced Jon Bernthal as Frank Castle. However, the sole significant downside to the season was Elodie Yung as Daredevil's love interest Elektra.

Whenever she crops up, the story slows to a snail's pace and becomes needlessly tedious. Yung is clearly smart enough to recognize the inherent flaws of the character and tries to exaggerate her character's flaws in a valiant attempt to drown them in overexposure. It ultimately fails and so does the character. With Elektra currently regenerating in a clay jar, now is certainly the time to find a new actress to play the part.

4 GROOT

Groot

Groot is one of the best parts of the Guardians of the Galaxy series, both in his fully grown and baby forms. Vin Diesel brings no small amount of star power to the role, but his voice is so altered in editing that he might as well not have been hired. Baby Groot's voice was so adorably squeaky he was practically a chipmunk and regular Groot's voice was so deep it sounded like eight Vin Diesels were speaking into the mic at once.

If so much editing was going to happen in post, it would make more sense to find an unknown actor who would be considerably cheaper to hire. All the editing would modulate their voice to the point that nobody would even know there had been a switch. In fact, is Vin Diesel still the one doing the voice? Have they made the switch already?

3 CASSIE LANG

Cassie Lang

Abby Ryder Fortson played Scott Lang's adorable young daughter in Ant-Man as a cute macguffin for him to strive for over the course of the film. She does well in the role, at least as well as any child actor can do, but by casting Cassie Lang so young, Marvel has unfortunately deprived itself of a valuable storyline.

In the comics, Cassie Lang becomes the hero Stature as a teenager, using a similar suit to her father's to attain the same powers, albeit with more focus on growing than shrinking. If Marvel were to replace Fortson with an older girl, they could hypothetically bring Stature to the MCU to fight alongside Ant-Man and Wasp, bringing along with it the beloved tropes of teenage angst, family dysfunction, and eventual reunion.

2 AUNT MAY

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The decision to cast Marisa Tomei as Peter Parker's Aunt May in Captain America: Civil War was a bit of head scratcher at the time. Tomei was too youthful to be the old, frail woman from the comics, but too aged to be the "older sister type" that Kevin Feige claimed they were aiming for. Tomei is a talented actress and brings a lot to her performances in both Civil War and Spider-Man Homecoming, but her caught-in-the-middle status is a distraction throughout.

Tomei herself was appalled to learn how old the character was in the comics and suggested she might not have accepted the role if she'd known. Recasting this role may be difficult to explain, but choosing to go with a much significantly older would certainly clear up any misunderstandings.

1 SPIDER-MAN

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This feels particularly cruel seeing as how Tom Holland's Peter Parker is still new to the MCU and is just coming off a successful film release. He's even a great actor in the role. The problem lies in the MCU as a whole. If you line up all the headlining heroes of the franchise, you'll notice that aside from Luke Cage and Black Panther, all the marquis players are white.

Marvel has something of a diversity problem and, despite what the comic executives think, the problem is not that they have too much of it. If Marvel wants to add more color to its film roster, the best place to do so is with Spider-Man. There are any number of stories than can tell which would remove Peter Parker and introduce film audiences to the living embodiment of Marvel's recent emphasis on diverse content, Miles Morales.

Disagree with anyone on our list? Hit up the comments and let us know your thoughts!