Being a part of the MCU is a huge achievement for any actor. The world that Marvel has built encompasses so many different characters, worlds, and stories, that there are plenty of opportunities for actors to really shine in their roles. It has even turned some actors into certified movie stars and given them a leg up to take on other roles that they might not have been considered for. It helped to turn Robert Downey Jr.'s career around and make him one of the highest paid actors in Hollywood. It has also given some actors a chance to really explore their range and show what they can do. Who knew that Dave Bautista was so incredibly funny and had great comedic instincts? Marvel chooses their actors carefully, and will often reach out to someone to offer them a role rather than having a lengthy audition process.

However, some actors in Hollywood have not been so eager to jump into the Marvel Cinematic Universe. They may have been offered roles, but they decided to turn them down in favor of exploring other opportunities or staying with their current projects. Sometimes this has worked out for the actors, as they still go on to do great things. Other times, it's entirely possible that an actor is secretly kicking themselves because they turned down a role that might have led to bigger and better things. Throughout the history of Marvel Studios, there have been plenty of "What if?" moments, with an actor being considered for a role that went to someone else. These are eight actors who probably regret turning down their Marvel roles (and ten actors who are doing fine without them).

18 FINE WITHOUT IT: SAOIRSE RONAN

At one point during the casting for Avengers: Age of Ultron, the name that seemed to be thrown out the most as being attached to the part of Scarlet Witch was none other than Saoirse Ronan. Ronan had already proven that she could play action fairly well with her role in Hanna, so she would have been a perfect fit.

It was reported that Ronan was actually Joss Whedon's first pick for the role. However, she eventually turned it down, despite expressing an interest in the film in a previous interview. Not that it was a bad decision. Ronan went on to star in Brooklyn which garnered her the first of two Oscar nominations, the next being for her role in Lady Bird.

17 PROBABLY REGRET IT: JENSEN ACKLES

Jensen Ackles, who has appeared in all 14 seasons of Supernatural, has really carved out a niche for himself. No one could blame him for sticking with the show, considering that it has always been steady work and has become a huge cult hit with a dedicated fan base. Still, it might have been nice to be involved with something bigger, and that almost happened for Ackles.

Jensen Ackles had auditioned for Captain America but lost out to Chris Evans. However, the Marvel folks liked him so much they offered him the role of Hawkeye instead. Ackles turned down the role, citing scheduling conflicts with Supernatural, which in retrospect seems like it might have been a misguided choice. Supernatural is great, but the Hawkeye role could have led to bigger, better things.

16 FINE WITHOUT IT: TOM CRUISE

Can you picture anyone other than Robert Downey Jr. playing Iron Man? It's difficult to separate the actor from the role at this point, considering he was the catalyst for the entire MCU but in early development, one other prominent actor had been attached to the role: Tom Cruise. Cruise had way more star power at that point, but it wasn't meant to be.

Plans for an Iron Man movie went a long way back, even into the '90s, and all the while, Cruise had been on board to play billionaire Tony Stark. However, when the time came to make the thing, he turned down the role due to commitments on the Mission: Impossible and Jack Reacher franchises. Cruise is still doing fine without the role, and Robert Downey Jr. turned out to be the Iron Man we needed all along.

15 PROBABLY REGRET IT: RACHEL MCADAMS

Rachel McAdams is one of two special cases on this list, in that she turned down one role in the MCU only to pick up another one. McAdams had originally been offered the part of Pepper Potts, Tony Stark's beleaguered assistant, and love interest. McAdams turned the role down, though, to make The Time Traveler's Wife. Gwyneth Paltrow ended up in the role and has done a fine job, overall.

McAdams wasn't out of the MCU forever, though. A few years later she was offered the role of Dr. Christine Palmer in Doctor Strange. Although she has only appeared in one film (so far), McAdams might have made the better choice. Palmer is a skilled surgeon who ends up saving the hero's life after he is wounded in a fight.

14 FINE WITHOUT IT: MADS MIKKELSEN

Mads Mikkelsen is practically born to play villains. Right from his breakout role in Casino Royale to his leading role in Hannibal, it's been obvious that the actor has the right look and instincts to play the bad guy. Marvel saw this and obviously offered Mikkelsen a part. Originally he might have been cast as Malekith in Thor: The Dark World, but he turned it down due to scheduling conflicts.

However, like Rachel McAdams, Mikkelsen wasn't going to stay out of the MCU forever. He was also eventually cast in Doctor Strange as the villain Kaecilius. That might have been for the best, as he may have been wasted in Thor: The Dark World, especially if they buried his incredible facial expressions under pounds of makeup.

13 PROBABLY REGRET IT: OLIVIA WILDE

Olivia Wilde has appeared in action films like Tron: Legacy and Cowboys and Aliens, so she would have been a natural fit for the spectacle of MCU films. Marvel knew this, which is why they offered Wilde the role of Gamora in Guardians of the Galaxy. Wilde, however, turned the role down for undisclosed reasons.

The role went to Zoe Saldana, who has done an excellent job playing the tough and reliable Guardian. Wilde may have turned down the role due to the fact that she did not see enough complexity in Marvel's female heroes. She might be regretting that choice now, as Marvel continues to explore and expand upon the stories of its most popular female characters.

12 FINE WITHOUT IT: JOAQUIN PHOENIX

Joaquin Phoenix has had his name thrown around at Marvel for several years. He was originally tapped to play the Hulk as Edward Norton's replacement, but he turned that role down. Next, he was offered a chance to play Doctor Strange, but he similarly turned that down. Phoenix has stated that he does not regret turning down the roles, though.

In an interview with Little White Lies, Phoenix said, "I think everybody was really happy with how things turned out. All parties were satisfied." That seems to be the truth, as the MCU has done fine (obviously) and Phoenix gets to keep appearing in interesting projects that challenge him.

11 PROBABLY REGRET IT: MATTHEW MCCONAUGHEY

Matthew McConaughy has had something of a career resurgence in the last few years, ever since his appearances in more ambitious productions like True Detective and Dallas Buyer's Club (which earned him an Oscar for Best Actor). McConaughey is a huge star, so obviously, Marvel thought he would be perfect to play a living planet.

That's right, before casting Kurt Russell, Marvel had approached McConaughey and offered him the part of Ego in Guardians of the Galaxy vol 2. However, McConaughey decided not to take the role, saying that he saw it as being an amendment to someone else's story. He did The Dark Tower instead, which may not have been the best alternative.

10 FINE WITHOUT IT: AMANDLA STENBERG

Amandla Stenberg may only be 20, but she has already made her mark on the world of film and social issues. She first proved herself when she played Rue in The Hunger Games, and she has only moved on to bigger roles. Her latest film appearance in The Hate U Give spoke to the inherent problems that exist for people of color in the United States.

It's no wonder, then, that the talented young actor was up for a role in Black Panther. She had been auditioning for the role of T'Challa's sister, Shuri. However, Stenberg took herself out of the running due to her own ethics. In a CBC interview, Stenberg said, "I feel like it would have just been off to see me as a bi-racial American with a Nigerian accent just pretending that I'm the same color as everyone else in the movie."

9 FINE WITHOUT IT: JESSICA CHASTAIN

Jessica Chastain has appeared in some really great films like Zero Dark Thirty and Molly's Game, and she could have been part of the MCU as well. Marvel had offered her the role of Maya Hansen in Iron Man 3, but the actor turned the role down due to some scheduling conflicts. It wasn't her only chance to appear in the MCU, though.

She was later offered the role of Janet Van Dyne in Ant-Man, but she turned that role down as well. She apparently did not just want to be the side character in someone else's superhero movie. Unfortunately for Chastain, Janet Van Dyne got her chance to be a hero in Ant-Man and the Wasp. Chastain has done fine for herself, though. She will appear in IT: Chapter Two and Dark Phoneix in 2019.

8 PROBABLY REGRET IT: MEL GIBSON

Mel Gibson has had a long and interesting career, appearing in many films and directing his own, as well. He received an Oscar for directing the film Braveheart (which also won Best Picture). Throughout his acting career, he has a lot of experience with Shakespeare, appearing in many of the Bard's plays as well as the film version of Hamlet.

It's no wonder then that Gibson was tapped to play Odin in the heavily Shakespearian Thor. However, the actor turned down the role. It worked out better for audiences anyway, who got to see the incredibly talented Anthony Hopkins take on the role, but maybe playing Odin would have given Gibson a chance to really shine and re-examine his life.

7 FINE WITHOUT IT: PATRICK WILSON

Patrick Wilson has a long resume of playing interesting characters, including appearing in two different comic book films: Watchmen and Aquaman. Wilson was even attached to Ant-Man, back when it was in the hands of Edgar Wright. His role was never revealed, but after constant delays with the film, Wilson eventually had to leave the project.

It wasn't a huge loss for the actor, though. Not only did he get to play a lead role in season two of Fargo, but he got to take on other projects as well. Obviously not being tied to the Marvel universe left him free to play Ocean Master in the DCEU, a much bigger and more prominent role than what he might have had in the MCU.

6 PROBABLY REGRET IT: ALEC BALDWIN

Alec Baldwin has had plenty of great roles throughout his career. He was one of the most memorable parts of Glengarry Glen Ross and he is only in one scene! Obviously, a star with as much experience as Baldwin would have been great in the MCU, and he was even offered a role at one point, but he turned it down due to his wife's pregnancy.

The role was never revealed, but it might have been good for Baldwin to appear in a Marvel film. It might have put him in a different direction than the one he is on now, and that could have been a huge benefit to the actor. There is still time, though, for the actor to appear in some kind of role in the MCU, if Marvel still wants him, that is.

5 FINE WITHOUT IT: JOHN KRASINSKI

John Krasinski, who has gone from playing Jim on The Office to being a full-blown Hollywood star also had a shot at being in the MCU. He was originally being considered for the part of Captain America, and even got as far as doing a costume test. However, when he saw Chris Hemsworth dressed as Thor, he knew it wasn't for him.

In an appearance on Conan, Krasinski said, "I went, 'I'm good. This is stupid. That's okay, I'm not Captain America." Krasinski might have made a fine Cap, but he's done well without the role anyway, landing the lead role in Amazon's Jack Ryan in addition to directing the critically-acclaimed A Quiet Place. There may still be room for Krasinski in the MCU. Fans have said they would love to see him play Reed Richards.

4 FINE WITHOUT IT: EMILY BLUNT

Emily Blunt is known for her work in all sorts of different films, but she appears to have a particular attachment to action and science fiction, taking roles in films like Looper and Edge of Tomorrow. It makes sense, then, that Marvel would approach her for the role of Black Widow back in 2010, a role Blunt had to turn down due to scheduling conflicts.

Later, Blunt was offered the role of Peggy Carter in Captain America: The First Avenger but had to turn it down again, due to more scheduling conflicts. Blunt has done just fine without being in the MCU, appearing in great films like Sicario and A Quiet Place, so it's no big loss. Although, fans have made some noise about her being cast as Sue Storm (opposite her actual husband, John Krasinski!), and who knows what the future holds...

3 PROBABLY REGRET IT: JOSEPH GORDON-LEVITT

Joseph Gordon-Levitt proved his comic book prowess when he played the character of Blake, who would be revealed as Christopher Nolan's version of (six-year-old spoiler alert!) Robin in The Dark Knight Rises. Later, he was offered the part of Peter Quill in Guardians of the Galaxy. However, he turned it down to take on a different comic book project: The Sin City sequel.

Needless to say, this was a bad decision. The movie was a critical and financial flop. Gordon-Levitt has even said he made a huge mistake turning down the part. It seemed to work out for the best in the end, though, as it's hard to think of a Star-Lord that isn't played by Chris Pratt. Gordon-Levitt tried again in an audition for Ant-Man but lost the role to Paul Rudd.

2 FINE WITHOUT IT: JASON MOMOA

It's hard to imagine anyone other than Dave Bautista in the part of Drax the Destroyer, but one other charismatic and jacked actor was up for the part: Jason Momoa. He might have gotten the role, too, but he ultimately turned it down. His reason was that the role was too much like everything else he had done already.

While the role of Drax ended up being so much more (which might actually be due to Bautista's at times truly hilarious portrayal of the character), Momoa did just fine for himself. He made a big splash in the DCEU when he first portrayed Aquaman in Justice League, and now he is headlining his own movie. Everything worked out for everyone, it seems!

1 PROBABLY REGRET IT: JOHNNY DEPP

Johnny Depp has made some questionable decisions in his life, and this may just be one of the worst for him. Back when casting was taking place for Doctor Strange, Depp was apparently heavily considered for the role and was even made an offer by Marvel. However, he had to turn it down due to his commitment to the Pirates of the Caribbean franchise.

Things seemed to turn out pretty good, anyway. Benedict Cumberbatch is a perfect Doctor Strange, playing and looking the part perfectly. As for Johnny Depp, he might be kicking himself over missing out on the opportunity to be a part of such a popular universe. Well, at least he got to play Grindelwald in Fantastic Beasts. That's something... right?