With 16 movies released thus far and Thor: Ragnarok right around the corner, the MCU is hands-down the biggest and most successful movie franchise ever. Looking back to 2008 when Marvel released its first two movies, Iron Man and The Incredible Hulk, it is hard to believe that almost a decade later the MCU has made so many successful superhero movies. When Marvel kicked off its cinematic universe, it was impossible to predict just how big the MCU would turn out to be. And the MCU owes much of its success to the amazing actors, who dedicate time and energy to bring these beloved comic book characters to life.

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Casting has always been Marvel’s strong suit and even some of their more controversial casting decisions have worked out surprisingly and extremely well. Over the years, a lot of big names have been rumored for various parts in the MCU and Marvel would often go after an actor or actress who they deem appropriate for a certain role. However, sometimes conflicting schedules or lack of interest on the actor’s part led to someone else being cast instead. The MCU we know and love could have been a lot different, had these 15 actors said yes to the MCU.

15 OLIVIA WILDE - GAMORA

Olivia Wilde Guardians of the Galaxy Gamora

The House alum, Olivia Wilde, whom you may also recognize from Tron: Legacy and Cowboys and Aliens, was Marvel’s and the fans' first pick to play the green-skinned assassin Gamora in Guardians of the Galaxy. Wilde was one of the final frontrunners for the part, alongside Gina Carano, Adrianne Palicki, who was later cast in a different Marvel role, and Zoe Saldana, who we now know as Gamora.

Reportedly, Marvel offered the role to Olivia Wilde, but the actress decided to pass on it. Wilde commented that female superheroes are expected to be too perfect and opted to star in another undisclosed movie instead. While we have no doubt that Wilde would have made an excellent Gamora, Saldana turned out to be the perfect fit.

14 MADS MIKKELSON - MALEKITH

Mads Mikkelsen Thor The Dark World Malekith

Mads Mikkelson, whom we now know as the villainous Kaecilius from Doctor Strange, almost become part of the MCU a lot earlier. Originally, Marvel wanted Mikkelson to play a different villain -- namely, Makekith The Accursed in Thor: The Dark World. However, Mikkelson had to turn down the offer because of scheduling conflicts with his new TV show Hannibal.

The role of Malekith the Accursed went to Christopher Eccleston instead, whose excellent performance sadly wasn’t enough to make the character more memorable. In hindsight, as far as Mikkelson is concerned, it all worked out for the best. His TV series Hannibal became a critically acclaimed award-winning show and Doctor Strange’s Kaecilius turned out to be a far more compelling and interesting villain than Thor’s Malekith.

13 TOM CRUISE - IRON MAN

Tom Cruise Iron Man Tony Stark

These days it’s almost impossible to imagine Tony Stark being portrayed by anyone other than Robert Downey Jr. However, plans for an Iron Man movie date back to the '90s and the actor attached to the role of Tony Stark was none other than renowned action superstar, Tom Cruise.

When Marvel finally decided to start building their cinematic universe with Iron Man, their first choice for the role of the billionaire playboy was Tom Cruise. Even though Cruise was committed to the role for a long time, he passed on Marvel’s offer due to overwhelming existing obligations on the Mission: Impossible and Jack Reacher franchises. In a way this was a win-win for everyone. Robert Downey Jr. showed that was born to play Tony Stark and Tom Cruise’s talents are being put into good use in various action movies.

12 ALEC BALDWIN - AN UNNAMED MARVEL VILLAIN

Alec Baldwin WInter Soldier Alexander Pierce

The beloved comedy actor, best known for his performance on the hit series 30 Rock, as well as his recent impression of Donald Trump on Saturday Night Live, was almost cast in the MCU. Considering Alec Baldwin's impressive career, it is not at all surprising that Marvel approached him.

While Baldwin did not disclose what role he was offered, he did say it was a villain. Judging by the timeline, our guess is either Alexander Pierce in Captain America: The Winter Soldier, or The Collector in Guardians of the Galaxy. Unfortunately, Baldwin had to pass on the role due to his wife’s pregnancy. Baldwin would have been an excellent addition to the MCU, and hopefully Marvel will get to cast him as a villain in one of their upcoming movies.

11 RACHEL MCADAMS - PEPPER POTTS

Rachel McAdams Iron Man Pepper Potts

Actress Rachel McAdams, whom we fondly remember as Regina George in Mean Girls as well as Allie in The Notebook, was at the top of Jon Farveau’s list when casting Pepper Potts. Marvel even offered the role of Tony Stark’s "Girl Friday" to McAdams, who turned it down to work on State of Play and The Time Traveler’s Wife.

Despite the overwhelming criticism of Gwyneth Paltrow’s casting for the role of Pepper Potts, we think it worked out well. Her chemistry with Robert Downey Jr. is actually rather strong and she managed to make the role her own. On the other hand, Marvel finally got Rachel McAdams to join the MCU as Christine Palmer in Doctor Strange, a role the actress found to be more appealing.

10 EMILY BLUNT - BLACK WIDOW

Emily Blunt Iron Man 2 Black Widow

Back in 2010, the MCU was just starting to develop and it was anyone’s guess as to how it would turn out. When casting Iron Man 2, Marvel approached the rising star Emily Blunt for the part of Natasha Romanova, aka Black Widow. However, due to scheduling conflicts with Gulliver’s Travels, Blunt had to turn them down.

The following year, Marvel went after Blunt once again. This time for the part of Peggy Carter in Captain America: The First Avenger. Again, the deal fell apart due to scheduling issues. Reportedly, Blunt was also on the short list to play Captain Marvel. While we have no doubt that Blunt would have been amazing in any MCU role, Scarlett Johansson and Hayley Atwell did an incredible job portraying Black Widow and Peggy Carter.

9 JESSICA CHASTAIN - THE WASP

Jessica Chastain Ant-Man The Wasp

The two-time Oscar nominee, Jessica Chastain was also in talks to join the Marvel Cinematic Universe. Best known for her exceptional performance in critically acclaimed movies such as Zero Dark Thirty, Interstellar and The Martian, Chastain was offered the role of Hope van Dyne, aka The Wasp in Ant-Man.

Reportedly, the actress turned down the role because it did not have enough superhero action for her taste. According to Chastain, an actor gets only one shot with superhero movies. Once you’re cast as a certain character, you are that character forever. And playing a "civilian" in a superhero movie was not something Chastain was interested in. We wonder if her decision would have been the same if she knew that The Wasp would become a titular superhero in the upcoming Ant-Man and the Wasp.

8 JOAQUIN PHOENIX - THE HULK

Joaquin Phoenix The Avengers Hulk

When Edward Norton, who played the titular superhero in Marvel’s The Incredible Hulk, left the franchise, the MCU was essentially without a Hulk for their upcoming movie The Avengers. Marvel wanted a big name to fill Norton’s shoes and went after Joaquin Phoenix. But, Phoenix turned down the role and the part went to Mark Ruffalo.

However, Marvel was still not done with Phoenix. This time they offered him the role of Stephen Strange and even got pretty far in contract negotiations, before Phoenix backed out. Phoenix has since praised the MCU, saying that while he did enjoy the movies, it is not something he sees himself doing. Although Phoenix is a great actor and his performance in the Oscar-winning movie Her was flawless, we have to agree that he doesn’t seem like the right fit for superhero movies.

7 JENSEN ACKLES - HAWKEYE

Jensen Ackles The Avengers Hawkeye

The star of the CW’s Supernatural, Jensen Ackles auditioned for the role of Captain America, but Marvel opted for Chris Evans as they felt he was a better fit for Steve Rogers. However, Marvel apparently took a liking to Ackles and offered him the role of Hawkeye instead.

Yet, Ackles was quick to turn down the part due to scheduling conflicts with his TV series Supernatural, and the role of Hawkeye went to Jeremy Renner. It is questionable whether Ackles was truthful about why he turned down the part. Surely, if his schedule allowed him to take on the role of Captain America, he could have just as easily taken on the role of Hawkeye. Or maybe Ackles just didn’t feel like taking Marvel’s consolation prize.

6 JASON MOMOA – DRAX THE DESTROYER

Jason Momoa Guardians of the Galaxy Drax

Out of all of the MCU movies, casting Guardians of the Galaxy proved to be the most problematic. Marvel’s first choice to play the monstrous, but kind-hearted brute, Drax the Destroyer was none other than Jason Momoa. At the time, Momoa was best known for playing muscular characters who don’t necessarily say much and Marvel saw him as the perfect actor to play Drax.

After auditioning, Momoa was offered the part of Drax the Destroyer and even got to put on the costume. However, Momoa pulled out of the movie after realizing he didn’t want to be typecast into these kinds of roles. He went on to state that he would be taking on roles that show him as "happy" because that’s how he wanted his kids to see him. So, this November, we will get to see Momoa’s fun and cheerful portrayal of Aquaman in DCEU's Justice League.

5 JOSEPH GORDON-LEVITT - STAR-LORD

Joseph Gordon-Levitt Guardians of the Galaxy Star-Lord

While casting Guardians of the Galaxy, Marvel wasn’t afraid to knock on the doors of big Hollywood stars, such as Joseph Gordon-Levitt. The actor was offered the part of Peter Quill, aka Star-Lord, but turned it down in favor of making the Sin City sequel, which flopped at the box office. Since then, Joseph Gordon-Levitt has gone on record to admit that he made a bad decision.

So, when casting for Ant-Man started, Levitt was determined to get the part. Levitt made it on the short list, alongside Paul Rudd. After a fierce competition between two truly amazing actors, the role went to Paul Rudd, on account that he helped write the script. And while both Chris Pratt and Paul Rudd are awesome in their roles, an actor of Levitt’s abilities would certainly make an excellent addition to the MCU.

4 SAOIRSE RONAN - SCARLET WITCH

Ronan The Avengers Age of Ultron Scarlet Witch

When news broke out that Marvel was bringing Scarlet Witch into the MCU, fans were overjoyed. And speculations on who should play such a major character started immediately. Eventually, the role went to Elizabeth Olsen, who is doing an amazing job. However, another famous actress came really close to playing the mutant, Wanda Maximoff.

The two-time Oscar nominee, Saoirse Ronan was among the shortlisted actresses for the role of Scarlet Witch and was even offered the part. However, Ronan was in such high demand that she had to pass on the opportunity to play Scarlet Witch due to scheduling conflicts with her other projects. Nevertheless, we hope this won’t be the last time Marvel goes after Ronan and we get to welcome her into the MCU very soon.

3 MEL GIBSON – ODIN

Mel Gibson Thor Odin

As unbelievable as it may sound, despite the bad reputation he has today, Mel Gibson was once a well-respected and in-demand actor. However, after slurring some foul words and running into trouble with the law quite a few times, he’s lost his status in Hollywood. Shockingly enough the family-friendly MCU apparently approached Gibson with a role in Thor.

According to Gibson, Marvel offered him the part of none other than the king of Asgard himself, Thor's father Odin, which Gibson turned down. While Gibson would’ve probably worked out fine for the role of Odin, we have to give the advantage to Anthony Hopkins. It is just difficult to imagine that Gibson would have been able to breathe that much class and poise into the role.

2 JOHNNY DEPP - DOCTOR STRANGE

Johnny Depp Doctor Strange

Casting Stephen Strange was no easy task. Before the role finally landed in the hands of Benedict Cumberbatch, it was offered to a few equally amazing actors. One of the names on the short list to play Sorcerer Supreme, and Marvel’s first choice, was Johnny Depp.

Marvel though Johnny Depp was a perfect fit for the part and went as far as offering him the role of Stephen Strange. At the time Depp was engaged on Pirates of the Caribbean and could not take the part due to scheduling issues. We can certainly see why Marvel thought Depp would've been perfect for the part. It would have been immensely entertaining to see Depp’s take on Stephen Strange. However, we must say that Benedict Cumberbatch ended up doing a great job.

1 MATTHEW MCCONAUGHEY - EGO THE LIVING PLANET

Matthew McConaughey Guardians of the Galaxy Ego

The incredibly talented Matthew McConaughey has become one of Hollywood’s most sought-after actors, so it should come as no surprise that the MCU went after McConaughey twice. The actor was first offered the role of Stephen Strange in Marvel’s Doctor Strange, but turned it down for undisclosed reasons.

The second time around, Marvel approached McConaughey with the offer to play Peter Quill’s villainous father Ego in Guardians of the Galaxy Vol. 2. However, due to conflicting schedules with Stephen King’s The Dark Tower, McConaughey had to pass on the role. Alright, alright, alright. Adding McConaughey to the MCU would be awesome, but he's a bit too young to play Chris Pratt's dad. Nevertheless, we hope Marvel doesn't give up on him just yet and we get to see Matthew in one of their upcoming movies.

So, do you think any of these actors would've been a better fit? Let us know in the comments!