Before the Marvel Cinematic Universe became the powerhouse superhero franchise that it is today, it was simply an ambitious Hollywood project that its creators hoped would blossom into something big. A superhero cinematic universe was something that had never been done before, and putting the MCU's now-infamous first credits scene with Nick Fury telling Tony Stark about "the Avengers Initiative" at the end of Iron Man was a big gamble back in 2008. Thankfully, as we all know, this payed off tremendously and has earned the MCU legions of fans who have stuck with the franchise for 10 years and counting.

While a lot of fans will agree that Phase One (the name given to the MCU's first six movie) is not as great or successful as following phases, they still remember that, without these films, there would be no Phase Two, Three, or Four (if that's what it'll be called). Even though it had its share of ups (Iron Man and The Avengers) and downs (The Incredible Hulk and Iron Man 2), they only serve as a reminder of how far the MCU has come.

However, while every filmmaker making an MCU movie today is under a lot of pressure to meet the standard set by previous movies, this doesn't mean that the original six films were any easier (after all, it was the first time superheroes were teaming up on the big screen), and behind-the-scenes drama was just as abundant then as it can be today.

So, without further hesitation, here are the 20 Crazy Details Behind The Making Of The MCU's Phase One.

 The Avengers was almost R-rated

MCU Phil Coulson

Until Deadpool was released in 2016, R-rated entries in a PG-13 superhero franchise were unheard of. However, if a particular scene in The Avengers had gone unedited, the MCU could've been the first franchise to do so. Speaking to Movies.com, Marvel Studios CEO Kevin Feige revealed that the first cuts of the movie submitted to the Motion Picture Association of America came back with an R-rating because of S.H.I.E.L.D. Agent Phil Coulson's demise.

"Well, whenever you impale somebody from their back and the blade comes out their chest, there are issues," he said.

Though edits were done to make the scene less graphic, this didn't make it any easier to watch for fans of everyone's favorite agent/Captain America fanatic.

 Iron Man began filming without a completed script

When it was released in 2008, director Jon Favreau's Iron Man not only drew critical acclaim and great box-office numbers, but it also served as a fine launching point for the MCU. However, it's a good thing that the producers were such big gamblers, since they began filming without a completed script. That's right, arguably one of the greatest superhero movies of all time was composed of a lot of altered scenes and improvisation (particularly with lead actor Robert Downey, Jr.).

"As a director, you understand the story, but from a writing perspective, the script usually isn't caught up yet to where the story has evolved to through storyboards, so you hit the set understanding what the scene is about, but how you get there is achieved in different ways," Favreau told SuperHeroHype. This wasn't bad for what Jeff Bridges called "a $200 million student film."

Idris Elba's casting in Thor drew controversy

Despite not having much to do, actor Idris Elba's all-seeing Bifrost gatekeeper was a welcome addition to the MCU for fans of superheroes, Norse mythology, and Elba's talented acting... but not for the Council of Conservative Citizens.

Comprised of supremacists, the U.S. group called for a boycott of 2011's Thor when Elba's casting was first announced.

"Marvel has viciously attacked the Tea Party Movement, conservative, and European heritage," the group reported (according to The Guardian). "Now they have taken it one further, casting a black man as a Norse deity in their new movie Thor." Elba's response was: "Thor has a hammer that flies to him when he clicks his fingers. That's OK, but the color of my skin is wrong?" Amen.

Scenes with Hulk's blood were some the toughest to animate in The Incredible Hulk

Visual effects studio Image Engine has been behind several hit movie and TV show effects since the '90s, including various superhero movies. Though 2008's The Incredible Hulk was not the success Iron Man was earlier that year, it still boasted some remarkable effects. However, while many will believe that Hulk and Abomination's show-stopping final battle had the hardest scenes to work on, Image Engine revealed that the most work went to two scenes involving Bruce Banner's blood.

The first happens when we see a drop of Banner's blood fall through the bottling plant before landing in a soda bottle (which is later consumed by Stan Lee), while the second happens when Banner is testing his gamma radiation cure on his blood. The scenes supposedly took over a year to complete, and, while they weren't the highlight of the movie, they certainly proved Image Engine's talent.

Mickey Rourke used his own money to add to his Whiplash role

It's a real shame things didn't work out so well with actor Mickey Rourke's involvement with 2010's Iron Man 2, especially since he not only put a lot of effort into the role, but a lot of money as well. According to Daily Record, Rourke was responsible for villain Ivan Vanko (aka Whiplash) having a pet cockatoo and $20,000 gold teeth (both of which he paid for himself).

He also toured a prison in Russia and spent three months perfecting his accent.

However, as he explained to Crave Online, Rourke's desire to "bring some other layers and colors" to Vanko's character didn't pan out. "Unfortunately, the [people] at Marvel just wanted a one-dimensional bad guy, so most of the performance ended up on the floor," he said.

The Incredible Hulk won an award for going green

Producer Gale Anne Hurd has been an advocate for a cleaner environment since her work with ex-husband James Cameron on 1989's The Abyss opened her eyes to the effects of pollution on the ocean. When she got the chance to work with Marvel's "green giant" a second time (after previously producing 2003's Hulk), she made sure that the blockbuster's production would be greener than the titular hero's skin.

According to Variety, contributions to the movie's cause included hiring an environmental consultant and decreasing plastic water bottle and utensil usage. Thanks to this, The Incredible Hulk became the first major motion picture to be awarded the Environmental Media Association's Green Seal.

Robert Downey Jr. hid food around Avengers set

Did you happen to notice Tony's eating habiys in The Avengers? Well, several fans did, and rumors began circling that Robert Downey, Jr. was bringing food and hiding it on set. This was finally confirmed by actor Vincent D'Onofrio (who continues to shine as Kingpin on Daredevil) in a HuffPost Live interview.

"Downey does hide food all over set," D'Onofrio said. "I'm not going to tell you why. But he does. It makes perfect sense."

While D'Onofrio has yet to be involved with the MCU's movie series (though that could certainly change in the future), he did star alongside Downey in the 2014 legal drama The Judge, so he's clearly been around him enough to know. Can we really blame Downey? After all, one can't save the world on an empty stomach.

One of Chris Hemsworth's brothers also auditioned for Thor...

While it's hard to imagine anyone other than actor Chris Hemsworth in the role of Thor, there were countless other actors who initially auditioned for the role.  According to Hemsworth, he missed out on the role with his first audition, but his younger brother, Liam, actually made it into the final few candidates.

"None of those guys got it," he told W Magazine. "My manager then called up and said, 'You know, he's got an older brother. Can we bring him back in?'" Hemsworth's second chance at an audition was definitely a step up, as he said he came in "kind of with a little, I guess, motivation and maybe frustration that my little brother had gotten further than me."

...and so did Tom Hiddleston

Before Tom Hiddleston became known for his portrayal of Thor's trickster brother, he actually auditioned for the God of Thunder. "So yeah, I was told I was being tested for the role of Thor and I had half a day, so in mid-March last year I came in and met Craig [Kyle] and met Ken [Branagh[ and did a test for Thor with Thor's blonde wig and facial hair and 20 pounds extra muscle which I managed to find somewhere," Hiddleston recalled to Collider.

While the producers found their Thor in Hemsworth, when Hiddleston heard they wanted to offer him the part of Loki, he "screamed and had to sit down on the pavement somewhere outside of a grizzly pub in North London." Hiddleston took quite the journey to become one of Marvel's greatest movie villains.

Chris Evans turned down the role of Captain America several times

Another actor who the MCU couldn't succeed without is Chris Evans. Thankfully, he put his not-so-hot days as the Human Torch behind him when he debuted as Marvel's World War II hero in 2011's Captain America: The First Avenger.

However, when he was initially offered the role, Evans was reluctant to accept such a huge contract.

"I was scared," he told Jimmy Kimmel. "In doing movies one at a time, if all of a sudden you decide you don't want to do it anymore, you're afforded the opportunity to take a step back and recalibrate. When you have a giant contract, if all of a sudden you're not responding well? Too bad, you got to suit up again." While Evans does have a great point, it's nonetheless a relief that he ended up finally accepting the role after discussing it with friends and family.

Elon Musk gave Robert Downey Jr. a tour of SpaceX during Iron Man

Robert Downey, Jr. certainly takes the role of Tony Stark seriously. Besides getting to explore an L.A. complex that once belonged to business and aviation icon Howard Hughes' company Hughes Aircraft, he also got to experience the work of SpaceX and Tesla CEO Elon Musk up close. According to Ashlee Vance, author of Elon Musk: Tesla, SpaceX, and the Quest for a Fantastic Future, Downey received a personal tour from Musk himself while visiting the nearby SpaceX headquarters.

Downey told Vance that Musk and Stark are pretty similar, in that they both "had seized an idea to live by and something to dedicate themselves to." Musk's impact on Downey was so great that he had a Tesla Roadster appear in Tony's garage in Iron Man. Musk also went on to cameo in Iron Man 2.

Physicists were brought in to help with Thor

During Thor's production, Marvel asked physicists Sean Carroll, James Hartle, and Kevin Hand to consult on the movie to help bring out its scientific side (which may have seemed difficult due to the film's inspiration from Norse mythology). One things that the physicists helped with was the Asgard's Bifrost, which works remarkably similar to a wormhole. However, when Kevin Feige told Carroll the term sounded "too '90s," he recommended calling it an "Einstein-Rosen bridge" instead, since it "means the same thing."

Both Carroll and Hand returned to consult on the 2013 sequel, in which Carroll advised the crew on the use of dark matter. "Marvel is very, very interested, with every movie they make, in trying to meet with scientists," he told Mother Jones. "With real-world sciences and the comic-book universe, they just try to make it all hang together."

Chris Evans wore a prosthetic jaw for the Avengers shawarma scene

In the now-iconic Avengers post-credits scene that shows Earth's Mightiest Heroes sitting down to enjoy some shawarma, eagle-eyed fans might have noticed that Captain America didn't touch his food. His face also looked a bit off in the scene.

Since the scene was added in after the movie's Hollywood premiere, the beard that Evans had grown for Snowpiercer had to be covered up with a special jaw prosthetic.

Evans also covered it up with his hands in order to make it less visible. However, this did not go without some jokes from his fellow cast members, particularly Robert Downey, Jr., who impersonated the Elephant Man as a reference for Evans' predicament. If only this had made it into the movie, too.

Edward Norton was uncredited for his Incredible Hulk rewrites

Anyone watching The Incredible Hulk for the first time will notice that Zak Penn is the only writer credited for the movie. However, star Edward Norton had actually rewritten Penn's original script, so what was the deal? Well, not only did Marvel end up cutting most of Norton's rewritten scenes, but the Writer's Guild of America ruled that he didn't alter the script much at all, so he went uncredited.

Since then, Norton has expressed his dissatisfaction with Marvel, telling the audience at Comedy Central's roast of Bruce Willis that "I wanted a better script." Meanwhile, Penn stated at a Comic-Con panel that he "wasn't happy with [Norton] coming to Comic-Con saying that he wrote the script." Perhaps this sheds some light on the real reason behind Norton's disagreements with Marvel, which led to him being replaced by Mark Ruffalo as Bruce Banner.

 Captain America: The First Avenger used four versions of Cap's shield

While it makes sense to have more than one version of movie props, Captain America's debut movie certainly came prepared with at least six different shields. Frequent MCU prop master Barry Gibbs discussed Cap's various shields with Newsday. These shields included the triangular shield that Cap first uses, as well as multiple designs of his iconic circular shield.

"We had the 'hero shield,' which was made of aluminum, for our beauty shots," Gibbs explained. "It's too heavy for day-to-day use but fine for close-up work. We then created a lighter shield that was aluminum-faced with a fiberglass back, for use on a daily basis and which doesn't pull the costume down when strapped to it. And then we had a stunt shield made of polyurethane." Two softer versions were also made in the event of stunts or accidents.

 New York City was digitally recreated for The Avengers

The final battle in The Avengers remains one of the most memorable showdowns in the MCU, which blew fans away with the realistic destruction of New York City. However, while the Chitauri and Leviathans were obviously fake, it turns out that most of the city shots were as well.

Since helicopters couldn't be flown low enough for desired filming, the Industrial Light & Magic effects team had to work for eight weeks, with four photographers constantly taking pictures on the streets of New York, before being combined and edited.

"It was the ultimate culmination of building on the virtual background technology [at ILM]," VFX supervisor Jeff White told FXGuide. As if getting all the Avengers onscreen together wasn't hard enough.

Sam Elliot wanted to return as General Ross

Before William Hurt's time began in the MCU, Sam Elliot was hunting the Hulk as General Thaddeus "Thunderbolt" Ross. While many would like to forget Ang Lee's version of the Incredible Hulk (probably due to its lack of action, odd creative choices, and poor CGI), Elliot seemed to enjoyed his time and wanted to return.

When actors from the 2003 movie gave MTV their thoughts on the 2008 reboot, Elliot stated he'd "loved to have done another one." However, he gave his support for the reboot and the casting of Edward Norton as Hulk. Still, it's probably for the best the MCU didn't use Elliot, as it would've confused fans about the connection between the two movies.

An unauthorized fan photo was cut from Iron Man home releases

Set photos are constantly leaked online for upcoming movies, but one particular photo of Iron Man caused quite the back-and-forth situation for Paramount Pictures. After freelance photographer Ronnie Adams' photo of Iron Man was uploaded to IESB.net, Paramount responded by getting the site offline. Following massive support and an interview with IESB editors Robert and Stephanie Sanchez, the site was back online and received "Iron Man press coverage, including interviews and a set visit," according to Collider.

When director Jon Favreau tried to make light of the situation by including the photo in the movie (attached to the "Who Is The Iron Man?" story on Tony's newspaper), Adams retaliated by suing Paramount and Marvel Studios. The picture was later taken out of home media releases, putting an end to a rather clever inside joke.

The Amazing Spider-Man almost crossed over with The Avengers

Oscorp Tower from The Amazing Spider-Man

Actor Tom Holland may be the MCU's official friendly neighborhood Spider-Man, but when Sony's Amazing Spider-Man series was still a thing, many fans dreamed to see Andrew Garfield meet up with Tony Stark and the rest of the Avengers.

While a crossover never came to pass, the two worlds almost collided in an unlikely way: the use of Oscorp Tower in The Avengers.

Producers Avi Arad and Matthew Tolmach told Latino Review that they came very close to doing this but scrapped the idea since "by the time the Oscorp building was fully designed, The Avengers' digital Manhattan was already basically rendered." Perhaps a new Oscorp building (along with a new Norman Osborn) will make its way into a future movie.

Robert Downey Jr.'s salary increased from $500k to $50 million

Robert Downey Jr. as Tony Stark uses Jericho Missile in Iron Man

There's no doubt that Robert Downey, Jr.'s overall MCU pay has been massive. However, many fans are unaware that it got really big really fast. According to The Hollywood ReporterDowney's work on Iron Man earned him $500k, which is a lot but not outrageous. However, after starring in another solo movie (and having a short but humorous cameo in The Incredible Hulk), Downey's amount for The Avengers ballooned to a massive $50 million payday.

This was reportedly due to Downey's representatives negotiating a set percentage for upcoming Marvel movies. In any case, even diehard MCU fans have to admit this is pretty insane (especially when compared to fellow Avengers Chris Evans' and Chris Hemsworth's seven-figure amounts).

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Are there any other secrets behind the making of MCU's Phase One that we forgot? Let us know in the comments!