Cassie Lang/Stature
Originally Played By: Emma Fuhrmann
Replaced By: Kathryn Newton
How It Went Down: While Fuhrmann initially took over the role of Scott Lang/Ant-Man's daughter from Abby Ryder Fortson (who appeared in Ant-Man and Ant-Man and the Wasp) after the MCU staged a five-year time-jump in Avengers: Endgame (turning Cassie into a teen), the studio announced in 2020 that Newton would be playing Cassie in Ant-Man and the Wasp: Quantumania.
While Cassie's appearance in Endgame was limited to just one scene, she becomes one of the main figures in the threequel, which is likely the reason behind the recasting.
"To us, after the events of Infinity War and Endgame, it really occurred to us that Cassie's going to be 18 in this movie! That's great!" director Peyton Reed told Nerdbunker. "The whole theme is time, and how much time he's missed, and his main motivation is just, 'I want time with my daughter.' I love the idea of Scott still relating to Cassie as a kid, but she's not. She's a young adult now, she has her own ideas about what it means to do good in the world, and she's trying to find her voice as a hero, and she can also be a little critical of her father."
Bruce Banner/The Hulk
Originally Played By: Edward Norton
Replaced By: Mark Ruffalo
How It Went Down: Has there ever been a more tumultuous role than that of Bruce Banner/the Hulk?
Initially, Eric Bana played the mean green machine in 2003's Hulk, which is not considered to be part of the MCU canon. When that film flopped both critically and at the box office, Marvel decided to reboot, with Norton taking over in 2008's The Incredible Hulk.
The film made $265 million but Norton and the MCU didn't seem to make for a potent pairing, with reports of creative differences resulting in his exit.
"We have made the decision to not bring Ed Norton back to portray the title role of Bruce Banner in the Avengers," Marvel said in a statement ahead of production beginning on The Avengers. "Our decision is definitely not one based on monetary factors, but instead rooted in the need for an actor who embodies the creativity and collaborative spirit of our other talented cast members. The Avengers demands players who thrive working as part of an ensemble."
Shots officially fired, with Norton's camp calling the statement "offensive" and "mean-spirited," and going on to deny the allegations, calling it a "financial decision" on Marvel's part.
Fortunately, Marvel eventually found the right fit in Ruffalo—and realized the character worked better in ensemble settings, not standalone movies. "Mark Ruffalo's Hulk portrayal set a lot of things right in a way that made us all very happy," Marvel president Kevin Feige said at a press conference.
"[Hulk is] my generation's Hamlet. Everyone's gonna get a crack at it before it's all said and done," Ruffalo once joked to Vanity Fair.
Thanos
Originally Played By: Damion Poitier
Replaced By: Josh Brolin
How It Went Down: When the Mad Titan made his film debut in the mid-credits scene of 2012's The Avengers, he was played by the stuntman. But when Thanos fully stepped into his role as the MCU's big bad in Guardians of the Galaxy, Brolin was the actor cast to make the iconic snap.
"We wanted somebody to be more than just the voice," Feige explained in a 2014 interview with Collider. "Josh did the performance as well. We were looking at a wish list of, 'Wouldn't it be great if' names, and his name was on it. And you look at his face and the performances he gives, he could be Thanos without any effects. He has that kind of face and that kind of gravitas to it."
Poitier would later make a brief appearance as a mercenary in 2016's Captain America: Civil War.
James Rhodes/War Machine
Originally Played By: Terrence Howard
Replaced By: Don Cheadle
How It Went Down: The Empire star originated the role of Tony Stark's best friend in 2008's Iron Man, but he was subsequently replaced by Cheadle over a contract dispute, which Howard infamously spoke out about during a 2013 appearance on Watch What Happens Live.
"This is going to get me in a lot of trouble, but it turns out that the person I helped become Iron Man, when it was time to re-up for the second one, took the money that was supposed to go to me and pushed me out," he said, referring to Robert Downey Jr. "We did a three-picture deal, so that means that you did the deal ahead of time. It was going to be a certain amount for the first one, a certain amount for the second, a certain amount for the third. They came to me with the second and said, 'Look, we will pay you one-eighth of what we contractually had for you because we think the second one will be successful with or without you. And I called my friend that I helped get the first job, and he didn't call me back for three months."
Asked where he stood with Downey (who has never publicly responded to Howard's comment) after the deal, Howard replied, "Oh, I love him. God's going to bless him." The former co-stars reunited months later at producer Brian Grazer's wedding and snapped a selfie. "Nice to see my old friend again," Howard wrote on Instagram, adding that "life's too short."
Johann Schmidt/Red Skull
Originally Played By: Hugo Weaving
Replaced By: Ross Marquand
How It Went Down: While the Lord of the Rings star "loved" playing the villain in Captain America: The First Avenger, his opinion of Marvel soured after a contract dispute regarding his potential return in 2012's The Avengers.
"They'd pushed back on the contracts that we agreed on and so the money they offered me was much less than I got for the very first one, and this was for two films," Weaving explained to Time Out in 2020. "And the promise when we first signed the contracts was that the money would grow each time. They said: 'It's just a voice job, it's not a big deal.' I actually found negotiating with them through my agent impossible. And I didn't really wanna do it that much. But I would have done it."
Ultimately, Marquand played Red Skull when the character returned as the Stonekeeper in Avengers: Infinity War and Endgame, and The Walking Dead alum also lent his voice to Ultron Sentries in 2022's Doctor Strange in the Multiverse of Madness.
Thaddeus "Thunderbolt" Ross
Originally Played By: William Hurt
Replaced By: Harrison Ford
How It Went Down: The Star Wars and Indiana Jones legend is set to join the MCU as the president of the United States in the upcoming Captain America: New World Order following Hurt's death at the age of 71 in March 2022.
The late Oscar winner originated the role in 2008's The Incredible Hulk, going on to appear in four more movies, making his final appearance in Black Widow.