Marvel Studios is renowned for its incredible casting. Even seemingly unorthodox choices at the time like Robert Downey Jr. as Iron Man or Chris Pratt as Star-Lord are met with universal praise after release, but the casting process is notorious for being rigorous and intensely competitive. Sometimes the rumor mill goes crazy with names that have never even expressed an interest in the part, but other times big names end up reading for a part or even getting as far as a screen test before the final casting choice wins out.

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Whether it comes down to scheduling issues, actors losing interest or Marvel just deciding they're not quite right for the part, huge stars often get passed over in favor of lesser-known names. In a slightly different world, our Marvel Cinematic Universe could look a lot different, but would a change of actor for our favorite superheroes ruin something great or make it even better? Perhaps we'll never know the answer to that question, but given Marvel's track record for casting, we're inclined to trust their judgment on the matter. For better or worse, here are 15 actors who nearly got cast as your favorite MCU heroes and villains.

15 TOM CRUISE AS IRON MAN

An Iron Man movie was in discussion as far back as 1990, and Tom Cruise was attached to the role from 1998 right up until the last minute. Kevin Feige even mentioned talks with Cruise in 2004, but after nearly 10 years on the hook, he had lost interest in the part, stating, "As it was lining up, it just didn't feel to me like it was gonna work."

It may not have gotten that far anyway, as Iron Man director Jon Favreau famously campaigned hard to Marvel Studios for Robert Downey Jr. to take the part, even overlooking much bigger names at the time such as Clive Owen and Sam Rockwell. Of course these days, we can't see anyone else fitting the role of Tony Stark better than RDJ, and the Mission: Impossible movies are always a fun ride, so no one's really disappointed in the way things worked out.

14 JASON MOMOA AS DRAX THE DESTROYER

Jason Momoa has made a name for himself playing muscular, tough-guy characters who don't say much, which according to the actor, was exactly why he didn't take the part. Jason Momoa auditioned for the role of Drax the Destroyer in Guardians of the Galaxy and even got a chance to audition with Star-Lord himself, Chris Pratt, but in the end, he decided he didn't want to be pigeonholed into a certain kind of "brute" role.

He also went on to say that he wants to start taking roles that show him as "happy" because he wants his kids to see him as a happy person on-screen instead of the angry, scary guy. That seems to fit with his recent casting as Aquaman in the DCEU, who appears to be more of a fun-loving type than anyone else on the Justice League.

13 MADS MIKKELSON AS MALEKITH THE ACCURSED

Before Mads Mikkelson landed the role of Kaecilius in Doctor Strange, Marvel wanted him for another villainous role opposite Thor as Malekith the Accursed in Thor: The Dark World. Marvel Studios reportedly not only offered him the role, but actually officially cast him before Mikkelson had to drop out due to scheduling conflicts with his show Hannibal.

Christopher Eccleston ended up taking the role of Malekith, and it probably worked out for the better for Mikkelson anyway. Hannibal went on to become a critically-acclaimed, award-winning series, and Doctor Strange's Kaecilius ended up being the far more memorable character, through no fault of Christopher Eccleston's. This is one of those cases that makes one wonder how different the final product would have turned out to be, but both villains ended up having fairly short lifespans in the MCU.

12 DAVID DUCHOVNY AS THE HULK

Before Mark Ruffalo and before Edward Norton, David Duchovny was touted as the frontrunner to replace Eric Bana in the role of Dr. Bruce Banner. He was originally tapped for the sequel to 2003's Hulk before Marvel decided to reboot the franchise to fit better with their connected cinematic universe.

Despite Duchovny apparently being a big fan of the character, Edward Norton ended up landing the role in The Incredible Hulk before a clash with studio heads ousted him from the franchise as well. Rather than bring Duchovny back into the mix, they hired Mark Ruffalo, who's done a fantastic job by all accounts. However, one has to wonder if The Incredible Hulk would have ended up as Marvel's mostly forgotten child if Duchovny had instead been cast in the first place.

11 JOSH HARTNETT AS LOKI

Back when Thor came out in 2011, Josh Hartnett was a way bigger name than Tom Hiddleston. In fact, Tom Hiddleston was something of an unknown entity with just a handful of television series and TV movies on his resume. Josh Hartnett was very interested, had a vocal internet campaign pushing him for the role and reportedly even met with director Kenneth Branagh who claimed he was on a very short list of frontrunners. But of course, Tom Hiddleston won in the end.

Loki ended up being one of Marvel's most popular (and longest lasting) villains, but even Kevin Feige has said that if Tom Hiddleston had not brought the character to life in the way he did in Thor, we probably wouldn't have seen much more of him beyond that one appearance.

10 JENSEN ACKLES AS HAWKEYE

Known mostly for his role as Dean Winchester on Supernatural, Jensen Ackles originally auditioned for the role of Captain America. Marvel didn't think he was quite right for Steve Rogers, but they reportedly loved his audition and placed him on the short list of actors considered for the Captain before it was eventually given to Chris Evans. In fact, they liked him so much that they came back to offer him the role of Hawkeye as a consolation prize.

Ackles would quickly turn down the role due to claimed scheduling conflicts with Supernatural, but if he was willing to take the role of the much more prominent Captain America, one has to wonder if he just didn't want to play second fiddle to Chris Evans who beat him out for the role he really wanted.

9 ASA BUTTERFIELD AS SPIDER-MAN

When Marvel Studios struck a deal with Sony Pictures to feature Spider-Man in the MCU, the quest for Peter Parker became one of the most hotly discussed topics in Hollywood. They wanted someone young, who could fill the role for years to come, growing up with Peter Parker on-screen. One of the names that ended up on Marvel's very short list of contenders for Spidey was Asa Butterfield, who had already impressed audiences in films like Ender's Game, Hugo, and The Boy in the Striped Pajamas.

It was even reported by various news sources that he had officially been cast as the web-slinger, just days before representatives announced that Asa Butterfield was out of the running, and Tom Holland would be Marvel's new Peter Parker instead.

8 LEWIS TAN AS IRON FIST

Iron Fist was surrounded by controversy from the get-go. Though Danny Rand was traditionally white in the comics, many people were vocal that an Asian actor be cast in the role to avoid the dreaded "white savior" trope. Recently, it was revealed that an actor of Asian descent did almost land the role of the sworn enemy of the Hand before they decided to cast him instead as the sworn defender of the Hand.

Actor Lewis Tan still got to appear in Iron Fist as Zhou Cheng, the drunken Kung Fu master who challenges Finn Jones' Danny Rand in episode eight, "The Blessing of Many Fractures." Finn Jones has received a lot of criticism for his portrayal of Danny Rand, though not all of it due to choices by the actor. Would the show have been saved if Lewis Tan was cast as the Iron Fist instead?

7 EMILY BLUNT AS BLACK WIDOW

Taking a role in the MCU is a good career move for any actor or actress, known to propel virtual unknowns straight to the A-list, but back when Iron Man 2 was casting its Black Widow back in 2010, nobody really understood how much of a powerhouse the MCU would become. At the time, Emily Blunt was a rising star without any big movies under her belt yet, and when Marvel Studios offered her the role of Black Widow, she turned them down.

Her given reason was scheduling conflicts with Gulliver's Travels, which seems like one of the most unfortunate scheduling conflicts of all time. Marvel would again approach her for the role of Peggy Carter (which also fell apart due to scheduling), and her name was on the short list for Captain Marvel. Happily though, that scheduling blunder didn't stop her from making her way onto the A-list anyway.

6 JOAQUIN PHOENIX AS DOCTOR STRANGE

Emily Blunt wasn't the only person to be offered a major role from Marvel only to turn it down. Joaquin Phoenix was almost our Stephen Strange. Contract negotiations actually progressed pretty far, with most bets virtually guaranteeing he had won the role, before he backed out, and the role instead went to Benedict Cumberbatch.

One of the main reasons for his refusal was the future requirements for him to remain in the role, which might prevent him from taking on the more dramatic, arthouse films that let him develop his own characters rather than be told how to portray a role, which is a fair concern given Marvel Studios' hands-on approach with each of their superheroes. He still claimed he enjoys big blockbuster movies like the ones made by Marvel, but there's always more of a focus on events over characters.

5 OLIVIA WILDE AS GAMORA

Olivia Wilde has already proved her chops for a movie like Guardians of the Galaxy after appearing in Tron: Legacy and Cowboys and Aliens. She was an early favorite for Gamora regarding both fans and Marvel Studios alike, and was one of the final front-runners on a short list that included Gina Carano and Adrianne Palicki, who both ended up in other Marvel roles.

Marvel reportedly even went so far as to offer Wilde the role, but she decided to pass on it, saying that she felt she was playing too many "badass" women, in favor of another undisclosed film. The actress has never lacked for work in the years since, but none of them have been quite as successful as Guardians of the Galaxy.

4 GLENN HOWERTON AS STAR-LORD

Chris Pratt was regarded as a huge surprise in the casting of Star-Lord, which ended up working out spectacularly. However, James Gunn has said that if Chris Pratt hadn't gotten the role, it would have gone to an equally surprising choice, in the form of Glenn Howerton, who is most well-known for his role as Dennis Reynolds in It's Always Sunny in Philadelphia.

It's clear that James Gunn had a very specific type of actor in mind when he was looking for his Peter Quill, and it's one of those choices that makes you wonder how different the movie would have been if it went the other way. Dennis is more the self-absorbed, big-ego funny guy on Always Sunny, while Chris Pratt was known for his loveable goofball, Andy, on Parks and Recreation. It also makes you wonder if Glenn Howerton would have skyrocketed to A-list celebrity status in Pratt's place.

3 JOSEPH GORDON-LEVITT AS ANT-MAN

Joseph Gordon-Levitt has a long history of being rumored for possible casting as a superhero. From Batman to Peter Quill, Doctor Strange and yes, even Ant-Man. According to inside sources reported by Variety, Joseph Gordon-Levitt was one of the final two choices for Scott Lang in Ant-Man, along with the eventual winner, Paul Rudd.

Levitt has proven himself to be able to take on pretty much any kind of role, comedy and action included, but it seems that then director, Edgar Wright, wanted an actor who lent himself more exclusively to comedy, and no one can argue that Paul Rudd didn't absolutely nail the role. Still, we have to hope that Marvel keeps up the tradition of going back to actors they've already auditioned and considers Levitt for some role in the future.

2 TOM HIDDLESTON AS THOR

Wait, that Tom Hiddleston? The guy who ended up giving us one of the MCU's greatest villains yet as Loki? It's true: his first choice was Thor, and although it's hard to see him as anyone but Loki now, Marvel actually liked his first round of auditions so much that they brought him back for a full costume screen test, clips of which are available in the DVD extras of Thor: The Dark World.

Hiddleston bulked up significantly for the role and dyed his hair blonde, but in the end, he was "just not Thor." As great an actor as he is, this is one of those times we're glad it didn't work out, because otherwise, we wouldn't have him as Thor's mischievous brother, and Loki probably would have ended up another one-shot villain that never came back for The Avengers.

1 JOHN KRASINSKI AS CAPTAIN AMERICA

Though John Krasinski would eventually go on to play an action hero in 13 Hours, when Captain America: The First Avenger was being cast, he was mostly known for his role as the funny goofball, Jim Halpert on The Office. Marvel saw his potential though, and he ended up being one of the final candidates for the role of Steve Rogers, even getting a costumed screen test on a fully constructed set.

According to an interview with Conan O'Brien, he took himself out of the running when, moments before his screen test, he saw the chiseled Chris Hemsworth walk by and said to himself, "I'm good. This is stupid. I'm not Captain America." He's gone on record since then to say he loves the Marvel movies and is totally on board if Marvel wants to bring him in for any other characters.

Are any of these casting choices near-misses or near-hits with you? Let us know what you think in the comments!