Avengers: Infinity War just blew the roof off the box office, barely three months after Black Panther became one of the biggest films of all time. Yup, we can't get enough of Marvel movies.

But when it began 10 years ago this month, the Marvel Cinematic Universe -- which has expanded to 19 films, reinvented serialized movies, and made eye-watering amounts of cash -- was actually quite a gamble.

I am Iron Man

Back in 2008, Iron Man, the first MCU film, was far from a guaranteed hit. For starters, the Iron Man character had never appeared in a movie or live-action TV show, putting him behind the likes of Spider-Man and the Hulk in terms of general public awareness. And the big thing at the box office back then was the gritty and grounded Dark Knight series, which self-consciously played down its more comic book-y elements. Colorful and fantastic movies like Green Lantern and Ang Lee's Hulk were just as likely to flop as hit big.

As if that wasn't enough, Marvel brought in two guys to head up Iron Man who were definitely gambles.

"In the late 1990s Robert Downey Jr. was uninsurable," says box office analyst Stephen Follows, "making him unemployable to any production which wanted to get a completion bond." Despite being an Oscar-nominated actor, Downey had never fronted a blockbuster like this -- and neither had director Jon Favreau, the guy from Swingers, whose main directing experience was Christmas comedy Elf and a largely overlooked Jumanji sequel.

Multiple writers worked on drafts of the screenplay, only for Favreau to encourage Downey and the cast to improvise. The lack of a definite script didn't initially impress co-star Jeff Bridges, who only relaxed when he decided to view the chaotic production as a "$200 million student film."

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Ah yes, the money. Marvel had spent decades farming its comic characters out to other companies for TV and film adaptations, with mixed results. Even when a character hit big at the movies, Marvel didn't necessarily see big returns. Spider-Man was off making money for Sony hand-over-webshooter, while the X-Men were raking it in for Fox. So in the 2000s, the folks at Marvel's movie arm clawed back the film rights to their characters and borrowed a chunk of money from Merrill Lynch to make their own movies.

Iron Man was the first of this new series of Marvel-made movies. "I really don't know how people are gonna react to this thing," Favreau admitted shortly before the film's release. "This could be anything from a flop to ... something beyond people's expectations. You never know."

10 years ago today, the Marvel Cinematic Universe began. #IronMan pic.twitter.com/yKgEnCiyST

— Marvel Entertainment (@Marvel) May 2, 2018

As it turned out, Downey's insouciant charm carried the movie. Premiering on April 18, 2008 in Australia and May 2 in the US, Iron Man delivered a combination of humor, spectacular visual effects and unapologetic comic book action that made it a sensation with fans and critics.

More Marvel

Still, Marvel movie boss Kevin Feige had an even bigger gamble in mind. In Iron Man's final scene, Samuel L Jackson turned up as comic book superspy Nick Fury, setting the stage for Marvel's other superheroes to follow Iron Man onto the big screen.

The Marvel Cinematic Universe was born.

But just weeks later, in June 2008, the second MCU movie, The Incredible Hulk, opened to a lukewarm reception. According to Box Office Mojo, it remains the MCU's weakest performer -- and this was a character that mainstream moviegoers might actually have heard of.

As Marvel's disastrous 1986 Howard the Duck movie proved, Marvel's comics are full of characters who could be just a little too out there for mainstream audiences. Even the most devoted superhero movie fan might have been puzzled to see familiar caped crusaders fighting alongside viking god Thor or mustachioed magician Dr Strange --  and that's before you get to the real weirdos like Ant-Man, Groot and Rocket Raccoon.

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Hollywood often appears a bit embarrassed about the characters it brings from page to screen -- look at all the black body armor replacing capes and tights in the X-Men and Dark Knight films, for example. But Marvel went all in on the colorful capers of its superheroes, from Captain America's World War II origins to, well, just about everything in Guardians of the Galaxy.

Marvel continued to perfect the MCU's colorful, boisterous tone in 2011's Thor and Captain America: The First Avenger. "God forbid those films had [flopped]," Feige told Entertainment Weekly, because those solo outings primed audiences for the next big gamble: bringing those heroes together.

Avengers assemble

In 2012, the various heroes of the MCU met in The Avengers, shepherded by writer and director Joss Whedon. Crossover stories uniting multiple characters are common in comics, but rare in the movies -- at least in recent years.

"In the last couple of decades, traditional Hollywood studios have increasingly relied on sequels, reboots and remakes in order to provide what they hope will be sure-fire hits," explains Stephen Follows. "What we're seeing with Marvel is something else. They're similar to a model Hollywood loved 80 years ago: the film series' of the 1930s and 1940s."

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With Black Panther, Avengers: Infinity War and Ant-Man and the Wasp all hitting screens this year, critics including James Cameron have warned of superhero fatigue. Marvel has a way to go to beat the most prolific film series of the past, however: There were 64 films featuring the Durango Kid between 1945 and 1952, an average of more than 9 a year.

Even if superheroes do start to lose their luster, the general industry trend of growing global box office spreads the risk of each new super-outing. "The first crop of MCU movies relied heavily on the domestic market," Follows says. "But as time has progressed, the international market has increased in importance." While Iron Man, The Incredible Hulk and Iron Man 2 made half their money in the US and Canada, by the time Spider-Man: Homecoming and Thor: Ragnarok hit screens two-thirds of their money came from overseas.

Inspired by the Marvel model, other studios have tried to create money-spinning cinematic universes of their own. Universal brought their classic monsters back from the grave with dubious success in The Mummy, while Marvel's comic industry rival, DC, attempted to fast-track its own crossover with Justice League. But none has managed to capture the magic of the MCU.

Marvel forever

After the success of the better-known names in the Avengers lineup, Marvel could have stuck to churning out Iron Man, Captain America, Thor and Hulk sequels. "A lot of studios would love to have four franchises they can keep doing sequels to," as Feige puts it. "We specifically didn't want to do that, because we wanted to keep bringing new characters to the forefront."

And so the Avengers paved the way for even riskier titles. Even among comic fans, who could name a single Guardian of the Galaxy before that movie came out? But by then, the Marvel brand was known as a mark of quality, even if you hadn't heard of the heroes in question. As each new film dropped, left-field directing choices such as James Gunn, the Russo brothers and Taika Waititi turned out to be pretty smart gambles.

When Black Panther exploded into theaters in February, it rocketed past a billion dollars and become a genuine cultural phenomenon. Not the most obscure comic hero but not the best-known either, Black Panther was just the latest example of Marvel banking on a character that might have been considered a gamble 10 years ago.

In 2019, Brie Larson's Captain Marvel will be Marvel's first female lead, and there are plenty more popular comic characters where she came from. Namor, Ms. Marvel, Nova, Moon Knight and many others have yet to appear on the big screen. And after Spider-Man's entry to the MCU, other well-known characters like the X-Men and Fantastic Four could be brought back into the fold following Disney's deal with Fox, current owners of those franchises' film rights.

Whatever happens next, let's hope Marvel isn't done taking risks.

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