The Marvel Cinematic Universe has built a reputation around employing stars at every point of their career. Robert Downey Jr. had one of Hollywood's best comebacks when he played Iron Man and became the heart of the MCU. Likewise, actors like Chris Hemsworth and Simu Liu essentially became A-listers after playing MCU superheroes. RELATED: 10 MCU Characters Most Likely To Be SkrullsIn addition, young stars Tom Holland, Tatiana Maslany, and Iman Vellani all joined the MCU as headliner characters. But there are still a few key actors not yet in the MCU's orbit, from Hollywood superstars to up-and-comers. Many have lobbied hard on social media or in interviews for a chance to play an iconic Marvel villain or hero.

Simon Pegg

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Image via Rogue Pictures

The MCU initially considered Simon Pegg as the titular lead in Ant-Man. However, the studio cast Paul Rudd in the role, which has proved to be perfect. According to Screen Rant back in 2018, Pegg said he would like to play the British superhero Captain Britain. Pegg is not known as a leading action-man, but neither was Paul Rudd before joining the MCU. CinemaBlend wondered if the upcoming Secret Invasion could be a potential entry point for Pegg to enter the franchise.

Lana Condor

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Lana Condor as Jubilee wasn't given enough screen time in the most recent Fox X-Men movies. This could be rectified by having Candor return to the role in the MCU. Jubilee is the youngest member of the X-Men team, but was a beloved character in the '90s cartoon show, serving as the audience's point of view character. Condor has already expressed publicly she wants to return to playing Jubliee now that the character and the rest of the X-Men are owned by Disney, and can be introduced into the MCU.

John Krasinski

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It would be cool to see "Jim" from The Office finally play a hero in the MCU. There have long been rumors of John Krasinski's attachment to portraying the leader of the Fantastic Four, Reed Richards. Krasinski has even gone on record saying he'd love to play Reed.

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Reed Richards is one of Marvel Comics' most complex and brilliant characters, but often self-sabotages himself. Krasinski would bring humanity to the role of one of Marvel's most intelligent and egotistical heroes.

Timothée Chalamet

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According to a story from The Hollywood Reporter, Timothée Chalamet auditioned for the role of Spider-Man, which eventually went to Tom Holland, so the actor has shown an interest in the MCU. There's also no proof to show he's changed his mind, with Chalamet gushing over the latest trailer for the movie on his social media.

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Chalamet is a talented actor who started in indie dramas and now leads his own big-budget franchise in Dune. It would be great to see him play one of the many X-Men now that Disney has the rights to the legendary team. Maybe Gambit or Cyclops?

Adam Sandler

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Bradley Cooper has done a hilarious job giving life to Rocket Racoon in the Guardians of the Galaxy movies. Sometimes it sounds like Cooper is channeling the sarcasm common in Adam Sandler movies like Billy Madison or Happy Gilmore.

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So, it makes sense then Sandler auditioned for the roles of Rocket and Groot in the early 2010s. While he wasn't cast at the time, it could finally happen with Marvel looking into his availability.

Jessica Chastain

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According to Indie Wire, Chastain decided against portraying a supporting character in Doctor Strange and publicly said she wants to be a more prominent MCU superhero in the future. Chastain is a two-time Academy Award nominee and, if cast, would bring a well-respected process as an actor to the MCU. A few characters would fit Chastain's acting abilities, like Emma Frost or Medusa of The Inhumans.

Keanu Reeves

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Image via Warner Bros.

The newest installment of The Matrix hasn't even landed in theaters, and Keanu Reeves is already thinking about joining the MCU. He recently said, "It would be an honor. There's some really amazing directors, and visionaries, and they're doing something no one's ever really done. It's special in that sense in terms of the scale, the ambition, the production. So it'd be cool to be a part of that." Reeves is a hit at the box-office and has proven to be a superhero commodity in multiple films. There are currently no rumors linking him to any substantial casting opportunity, but that shouldn't stop fans from coming up with their theories.

Matthew McConaughey

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There have been long-standing whispers around Matthew McConaughey joining the MCU. McConaughey has gone on record that he wanted to play The Hulk, but Marvel passed, so the actor is already publicly on board with joining the MCU.

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McConaughey is at the right point in his career to play a charismatic and powerful villain such as Magneto or Norman Osborn. One of these roles could continue the success of the "McConaissance."

Janelle Monáe

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With the X-Men movie rights now under the MCU umbrella, it makes sense the studio will begin casting the actors who will portray the mutant team. Cheat Sheet has linked singer and actress Janelle Monáe to the X-Men Storm. Monáe has publicly stated she wants to join the franchise, and possess the stylish individuality to represent the weather-controlling character. And she has refined her acting chops in award-winning movies like Moonlight, making her an inspired choice.READ MORE: Hawkeye Movies in Order: How to Watch All of the Avenger's MCU Appearances So Far