A little over a decade ago, all Marvel Studios had in its catalog of potential movie stars was a third-tier armored hero and the movie rights to other JV-level supers: a thunder god, an American patriot, and a KGB assassin. In an attempt to pull itself out of bankruptcy in the late ’90s, Marvel sold the movie rights to its most popular comic book characters, including Spider-Man, the X-Men, and the Fantastic Four, to established entertainment giants like Sony and Fox.

Imagining Marvel, now a bona fide entertainment juggernaut, as an underdog is difficult, if not hilarious. But that was the situation Marvel was in back then, and it was dire.

Ten years and several billion dollar hit movies later (including the biggest movie of all time), Marvel is now the Goliath of the movie industry.

A lot of the credit, deservedly, goes to Marvel Studios President and Chief Creative Officer Kevin Feige and his cinematic strategy of interlocking films. By making each standalone movie fit into a larger narrative, Marvel turned each of its solo superhero movies into a must-see story.

It helps, too, that those movies were anchored by actors like a resurgent Robert Downey Jr, rising stars like the Chrises (Evans, Hemsworth, Pratt), and Chadwick Boseman, as well as established Oscar winners like Natalie Portman and Anthony Hopkins, and a respected veteran in Samuel L. Jackson. It also helps that Marvel made a huge team-up movie every four years or so, where all the heroes get together to hang out and beat stuff up together.

Feige, like a storied basketball coach, created a team that eventually became a dynasty. And like any dynasty, it has had its share of copycats (see: Justice League) and detractors (see: Martin Scorsese), though even its biggest critics will reluctantly admit that the Marvel Cinematic Universe is a winning formula.

But while Marvel’s cinematic strategy has truly been a grand design, it wouldn’t have thrived if its films didn’t also have heart.

Heart, in this case, is the emotional pull that makes these heroes more than just action figures. Like the very best Marvel comic books, the very best Marvel movies make you happy when a hero thrives in the face of a challenge and give you a sense of impending doom when everything’s going a little too right for them. We’re emotionally invested in these heroes because of who they are as people, their personal strengths and weaknesses, their triumphs and their failures.

At the center of Marvel’s grand design of creating action movies with a beating heart is its two marquee Avengers, Tony Stark (a.k.a. Iron Man, played by Robert Downey Jr) and Steve Rogers (a.k.a. Captain America, played by Chris Evans) — whose animosity turned to respect, eventually gave way to friendship, and from there, understanding. Their relationship and how it evolved through a decade of the heroes’ interconnected movies propelled Marvel from a competent filmmaking studio into an entire, well, cinematic universe, one that fans cared deeply about on multiple levels.

And when we look at the next 10 years of Marvel movies, the now-complete central human story between Tony and Steve will be missed. Marvel succeeded in getting audiences invested in that relationship, but the thing about Marvel is that, nowadays, the studio has experience in selling us on stories about heroes, popular and obscure. And hopefully for audiences, Marvel will continue to give some soul to its ongoing assembly line of hits.

Tony Stark was impossibly relatable for someone who shouldn’t be

In the world of Marvel, Tony Stark is a rich and popular playboy, a man who’s invited to every party and wanted at every event. He’s not an underdog, and though he’s a celebrity, he’s not truly an aspirational one. Tony Stark is a genius who made his billions by selling high-tech weapons of destruction. He has blood on his hands from having armed the most dangerous people on Earth.

Stark is as irreverent and arrogant as he wants to be because, at the end of the day, he’s able to save the world. Because no one is smarter, savvier, more equipped with gizmos, ingenuity, and tech to save the world than Tony Stark.

Prior to his movies, however, both Stark and Iron Man had little name recognition among more casual comics fans. The bet Marvel made was to take this relatively obscure, prickish hero and turn him into the core of their entire cinematic universe. And what made that bet successful was how fallible he could be, an aspect that Marvel homed in on for the big screen.

Stark’s weakness isn’t kryptonite or some kind of superhuman ailment, but rather his own arrogance, stubbornness, and selfishness. Watching him work through his own worst traits is relatable, if not aspirational. There’s something reassuring about even a multi-billionaire genius not being able to use his money or intellect to cure his own arrogance. It makes him feel a little less powerful and a little more like us.

Stark’s story, from his very first movie, has been about coming to terms with his father’s legacy while also reckoning with his effect on the world. Howard Stark was seen as a visionary world-changer and had, throughout his life, worked alongside heroes like Captain America to save the world.

Stark carved out his own niche by bucking his dad’s legacy. He defies orders, like the government directive to keep his identity a secret, or in instances like 2015’s Avengers: Age of Ultron, when he thinks himself better equipped to protect the world than anyone else on Earth — a plan that ends with a defense project Stark was building gaining sentience to become a supervillain named Ultron, who’s threatening to eliminate life on Earth.

As unlikable as he seems on paper, Stark was beloved by fans (2013’s Iron Man 3, Stark’s final solo movie, is one of Marvel’s top box office performers of all time). A huge part of that is a testament to Robert Downey Jr’s effortless charisma and performance. But it’s also a matter of the gulf of difference between who Tony is on paper and who he is as a person and the difference between someone being likable and lovable.

Even if regular folks — the non-rich and/or non-famous — like us couldn’t relate to his lifestyle, there’s something relatable in Tony being consumed by the worst parts of himself. There’s something inspirational in seeing him want to overcome it. And while he flexed the worst bits of his arrogance and cynicism in each movie, he also wanted to become a better man.

Stark defeating the villains was also about defeating his own demons: his ego, his damaged relationship with his father, his irreverence for any kind of authority, etc.

And it’s his humanity that makes the end of Stark’s journey in Avengers: Endgame a heroic tragedy.

Eleven years since the Marvel Cinematic Universe kicked off with the story of Iron Man, Stark has made peace with his biggest failing: He was unable to stop the mad titan Thanos from obtaining all the powerful Infinity Stones and eliminating half of all life in the universe.

By the start of Avengers: Endgame, the final chapter in his story, Stark has let go of most of his ego and understands he can’t control everything — that he’s not an all-powerful being just because he has all the money in the world.

He has a family, a well-furnished, Nancy Meyers-approved mountain lodge, with an adorable daughter and one of those fancy rustic sinks. There’s nothing else he could want. But with his back against the wall in the film’s final fight, he finally realizes he must sacrifice himself for everyone else in order to truly stop the ultimate evil: Thanos, an intergalactic being who has harnessed the most powerful objects in the world to gain the ability to obliterate half the population with the snap of his fingers.

Stark’s sacrifice may have come off as a shocking twist to viewers, however. The shock doesn’t stem from the fact that his sacrifice is an act of good — we’ve seen him become a better man with each film. But rather, it’s the magnitude of the sacrifice of a man that viewers had considered to be too selfish to be a true hero that is a surprising, moving development.

Most importantly, it’s an earned one. In sacrificing his own life for others, Stark finally overcomes his own weaknesses and cements his legacy as a hero Stark himself could believe in. We’ve watched his story build toward Stark shedding his ego completely. In death, he does so.

Endgame represented a decade-long evolution and emotional depth of the character that’s unique to Marvel movies and a rare event in cinema in which we’ve followed a continuous narrative about one character for years of movies. Stark has grown up, become a hero who’s a far cry from the man we first met in 2008, and he and Marvel have taken us on an emotional journey alongside him.

Steve Rogers was the hope we needed

The greatest switch that Marvel played on us was killing off Tony Stark. What the studio initially made us all believe was that it was Captain America whose story was going to conclude in Endgame with a heroic sacrifice. After all, in the movie right before Endgame, Avengers: Infinity War, Steve Rogers’s most notable moment was when he tells the sentient, near-omnipotent android Vision that Avengers don’t “trade lives” — that he won’t let Vision die in order to stop Thanos. Anyone familiar with the way comic books work knows that it’s pretty much a rule that, when someone makes a grandiose speech like that, they will be the person who trades their life for others.

Marvel set up this bait and switch over nine years of movies: patriotic do-gooder Captain America would be that guy. In the comic book world, Cap was better known than Tony Stark in the late ’90s and early 2000s, but at the time was nowhere near as popular as Marvel’s premiere heroes like the X-Men.

While Rogers’s first official MCU appearance was as an emaciated weakling-turned-super soldier in 2011’s Captain America: First Avenger, he truly becomes the Captain America Marvel fans recognize from the comics and fell for in movies like 2012’s Avengers, 2014’s Captain America: Winter Soldier, and 2016’s Captain America: Civil War.

More than a muscly patriot, he was a hero with a strong moral conscious balanced out by a tragic longing for his past. Rogers has the jawline, strength, speed, abs, shoulders, and near-invulnerability of an exceptionally gifted man at his peak. But he’s still the scrappy, scrawny guy he once was underneath all of that. Socially, he’s also odd: He’s a man from World War II, someone from our grandparents’ generation, living in the present day in Chris Evans’s chiseled body. He knows no one in this world he’s been magically transported to, and that often includes himself.

Jokes about Rogers not getting references or technology or his distaste for foul language are peppered throughout the movies, but the humor is an avenue to a more serious and thoughtful picture: Rogers’s optimism and his ideas about heroism and duty are relics of an era that’s passed him by. He’s a relic himself, but one modern folks can respect; there’s nothing audacious or mythical about Rogers except his utter lack of pretense.

Rogers is the inverse of Stark, in that his defining character trait is his goodness. He’s the guy who will always be there for you whenever you need him. In his first movie, he literally crashed his airplane into the ocean to save the world, and ever since then, he’s been willing to do anything and everything to protect everyone, from Scarlet Witch and Vision to Sokovian civilians.

But that earnestness could easily skew toward cheesiness — hence the popularity of grittier heroes and Stark’s cynical and sardonic personality. What keeps Rogers from straying into cheeseball territory is that he carries with him the profound loneliness of leaving everyone he’s ever loved in the past.

His muscles, his super strength and agility, and that super-soldier serum can’t fix that isolation.

Rogers’s buoyant hope and indomitable spirit don’t come off as cheesy or saccharine, however, but genuine, admired, and almost wistful. They’re also defense mechanisms. If Rogers didn’t believe in hope, in trying to make the world a better place, it feels as though there’d be nothing keeping him from dwelling in his own sadness.

Rogers’s journey is about being a kind man and a good soldier in a world where those qualities are not valued or seen as something to be taken advantage of.

Steve Rogers and Tony Stark’s broken friendship throttled the MCU

Five years after the first Captain America movie, Civil War finds Rogers at odds with everything he’s believed. Rogers finds out that Bucky Barnes, his best friend who he thought died back in World War II before resurfacing in Winter Soldier, has been saved and brainwashed by the villainous worldwide organization known as Hydra. Hydra has been using Barnes in special missions and assassinations, including the assassination of Tony Stark’s parents.

Country, duty, law — the values that Steve Rogers cherished so much — are put on hold for his desire to help a treasured friend, the only one still alive from his past life. Under any other circumstance, Rogers would follow good soldier protocol and let the authorities deal with a criminal like Barnes. Rogers was taught never to put himself and his desires above all else, so bucking all that represents a total shift in the character we knew.

In protecting Barnes, Rogers also damages his friendship with Tony Stark.

Marvel spent movies and years developing Rogers and Stark, but also spent as much time developing their friendship. The only thing Rogers and Stark have in common is that they’re both heroes, and their disparate views of goodness and heroism is a hurdle when the two meet each other in 2012’s Avengers.

At first, Rogers sees Stark as phony, with no sense of duty and no respect for those who came before him. The resentment bubbles up in Avengers, when they’re both in the presence of their enemy Loki’s mind-bending scepter. It turns the Avengers against each other, bringing out their frustrations. Rogers’s and Stark’s dysfunctional friendship takes center stage.

“Big man in a suit of armor,” Rogers scoffs, an uncharacteristic moment of uncharitableness from Captain America. “Take that off, what are you?”

“Genius. Billionaire. Playboy. Philanthropist,” Stark jabs back, explaining that he’s created his own success, unlike Rogers who volunteered himself as part of the super-soldier experiment.

“I know guys with none of that worth 10 of you,” Rogers says. “I’ve seen the footage — the only thing you really fight for is yourself.”

With this animosity in the open, the two begin an unlikely truce over their next six movies. They know each other’s insecurities, weaknesses, and hold each other to account. Fighting alongside one another helps bolster their friendship, as they see the best in one another; they may not always agree, but they forge a shared reverence.

In Civil War, they don’t agree on a piece of legislation that would require them to register themselves with the UN (Stark wants to comply; Rogers doesn’t). Both know they won’t change one another’s mind, but they ultimately respect each other’s decision.

The point of no return happens not because of their opposing viewpoints on the law but because Stark finds out that Barnes killed Stark’s mom. Stark is determined to enact revenge. Rogers, to Stark’s utter disappointment and shock, joins the fight on Barnes’s behalf — going against his teammate to put his own friendship and past above his heroic duty and their friendship.

“You know I wouldn’t do this if I had any other choice,” Rogers tells Stark, explaining his decision to defend Barnes. “But he was my friend.”

“So was I,” Stark responds.

“That shield doesn’t belong to you. You don’t deserve it,” Stark says after losing the fight against Barnes and Rogers.

This fight and this exchange calls back to that first Avengers dustup: one character telling the other who deserves what and who is worthy of being called a hero. The roles are reversed, though, with Stark now telling Rogers that he’s not fit to be a hero because he’s only thinking about himself and his friendship. Rogers seemingly agrees with him and tosses his shield away.

Rogers chooses his best friend over Stark’s wishes, his country’s safety, and his duty to the Avengers. He also throws his shield away — a symbol of him chucking his Captain America persona. But his selflessness established in the eight years of movies still pointed to Rogers being the hero most likely to put his life on the line in Endgame.

In one glorious moment during the film’s climax, Rogers straps his freshly broken arm into his shield (Stark gives him a repaired one at the beginning of the movie), standing alone against Thanos’s army. That’s exactly the type of man he is: Someone who will stand in the way of all evil to protect the greater good, no matter what. And it’s Rogers’s influence that gives Stark the courage to do the selfless thing and sacrifice himself at the end.

Rogers taught Stark how to be selfless and to believe in the goodness of people. Stark taught Rogers to appreciate that there are things in this life that outrank duty. And their friendship is one of the most enduring stories Marvel has told.

Where does Marvel go from here?

When we look back at the decade of Marvel, we see a wildly successful run of 23 movies, each one seemingly more massive than the one before it. But with the conclusion of Endgame, the heart and soul of that success is now a legacy.

Tony Stark and Steve Rogers’s friendship defined 10 years of Marvel much more than any one razzle-dazzle battle, villain, or monumental world-saving moment. Marvel used the pair to tell a story of how the people in our lives, sometimes the ones who challenge us the most, can make us be better people than we ever thought. Perhaps even be heroes.

That emotional push and pull elevated Marvel beyond regular superhero fare. The Marvel Cinematic Universe isn’t good just because it has amazing special effects and jaw-dropping stunts or a system of interlocking movies; its magic stems from Marvel finding a way to make its superheroes human.

And now, with both heroes gone, it will allow for new stories to step forward in Marvel’s Phase 4.

Marvel’s cupboard isn’t bare. It’s brimming with potential and exponentially more possibility than it has 10 years ago, hanging its existence on a little-known hero and some of his amazing friends. Who knew then that a simple friendship could be the cornerstone of a universe many fans have come to love without limit? But I do wonder if Marvel will ever be able to create a narrative as rich as this decade-long story about friendship and the power it has to make us better — even super. I sure hope so.