The Marvel Cinematic Universe is easily Avengers movies are the glue holding it all together.

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There are a number of factors that have contributed to these movies clicking with such a wide audience – they’re escapist cinema, they’re pure spectacle, they’re full of payoffs – but arguably the biggest reason for their success is the complex relationships developed between the characters over time. Let's take a look at some of the most adorable friendships that emerged within the Avengers, as well as some that had potential but just didn't quite work out.

10. Sweetest: Tony Stark and Bruce Banner

Tony and Bruce talking in The Avengers

Thanks to soured on a lot of Joss Whedon’s contributions to Earth’s mightiest heroes. Still, one inspired choice that he made was building a friendship between Tony Stark and Bruce Banner.

In the comics, these two don’t really have much of a relationship, but Whedon realized that it makes sense that they would bond over being the Avengers’ only two scientific geniuses. Stark and Banner have respected each other since they first met on the Helicarrier, and it was always a joy to see them share the screen.

9. Never quite worked out: Quicksilver and Hawkeye

Hawkeye watches Quicksilver die

All throughout the two-and-a-half-hour epic that is Avengers: Age of Ultron, Quicksilver and Hawkeye’s relationship – which, based on the fact that Quicksilver triumphantly sacrifices his life to save Hawkeye in the movie’s third act, was intended to be one of the emotional cores of the film – never extends beyond one repeated line.

Quicksilver tricks Hawkeye and says, “you didn’t see that coming?” Later, Hawkeye tricks Quicksilver right back and says, “you didn’t see that coming?” In the end, Quicksilver gives his life to save Hawkeye and with his dying breath, he says (you guessed it), “you didn’t see that coming.” Hawkeye named his son after Quicksilver (his name is revealed to be Nathaniel Pietro Barton), just based on that.

8. Sweetest: Natasha Romanoff and Clint Barton

Black Widow and Hawkeye in The Avengers

Black Widow and Hawkeye are the only two who were friends before Nick Fury assembled the Avengers, because they were completing missions for S.H.I.E.L.D. across the world (including one memorable experience in Budapest) long before then. Across the Avengers saga, we’ve seen them bond over being the only two out of the core six heroes not to have any superpowers (okay, technically Tony Stark doesn’t have superpowers, but with nanotechnology, he might as well have).

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Their friendship is much closer than that, though. We’ve seen Clint’s kids call Nat “Auntie Nat,” and how torn up Nat was to hear that Clint had been murdering criminals all over the world as “Ronin” in his family’s Thanos-inflicted absence.

7. Never quite worked out: Thor and Tony Stark

Thor strangles Tony Stark in Age of Ultron

While Thor bonded with Captain America over being old, battle-hardened soldiers who were out of touch with modern-day life, he never really built a relationship with Tony Stark. After Tony created Ultron and the murderous A.I. escaped into the world’s computer networks, Thor grabbed Tony by the throat and lifted him off the ground.

Tony told him to use his words and Thor said, “I have more than enough words to describe you, Stark.” That moment tells us everything we need to know about these characters’ relationship. Thor has very little respect for Tony, for the most part, and as a result, they never became friends.

6. Sweetest: Steve Rogers and Natasha Romanoff

Captain America and Black Widow stand together in front of Wanda and Vision in Avengers: Infinity War

Although they began their relationship as adversaries, with Cap unsure if he could trust Black Widow, Steve Rogers and Natasha Romanoff grew into two of the closest friends within the Avengers. Starting with Captain America: The Winter Soldier, they became unbreakable allies.

That movie strengthened their bond and it would continue to grow for years to come. They trained the new Avengers together at the end of Age of Ultron, Nat let Steve go in to form the Secret Avengers, and Cap comforted a devastated Nat following the Snap.

5. Never quite worked out: Bucky Barnes and Sam Wilson

Sam Wison driving with Bucky Barnes sitting behind him in Captain America: Civil War

There is hope for this pair yet, since they’re about to star in their own double-act series on Disney+ called Midnight Run-like buddy cop tone, rather than smoothing it over and turning them into bona fide pals.

Since Bucky was brainwashed to ruthlessly try to kill Sam and Sam replaced Bucky as Captain America’s best friend, they both have a reason to hate each other, and they regularly remind each other of that fact.

4. Sweetest: Thor and the Hulk

Thor and Hulk sitting next to each other in a living quarters in Thor: Ragnarok

The Hulk may only have been included in Thor: Ragnarok because Marvel was unable to give him a solo movie, but his function in the film goes far beyond a loose adaptation of the “Planet Hulk” storyline. When Thor arrives on Sakaar, he’s in his lowest place, with Asgard hanging in the balance and pretty much everyone he loved dead.

Finding the Hulk there gives him a semblance of hope. Since the Hulk can’t communicate more than a few words and grunts, their relationship gave Thor time for some soul-searching. His friendship with the Hulk was played for laughs, but it was also very complex.

3. Never quite worked out: Ant-Man and War Machine

Giant-Man grabs Rhodey in Captain America Civil War

During the airport battle in Captain America: Civil War, Ant-Man experimentally enlarged himself to become Giant-Man, and grabbed War Machine out of the sky. Then, in Avengers: Endgame, when Earth’s mightiest heroes had resolved to all work together again following the apocalyptic devastation left in Thanos’ wake, War Machine jokingly referred to Scott Lang as “regular-sized man.”

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Based on these moments, there was the potential to develop Ant-Man and War Machine into a pair of good friends. However, despite Ant-Man risking his life to save War Machine (along with Rocket and the Hulk) from the wreckage of Avengers HQ, they never quite got there.

2. Sweetest: Tony Stark and Peter Parker

Tony Stark and Peter Parker walking side by side in Spider-Man Homecoming.

Some fans see Tony Stark and Peter Parker’s relationship as a surrogate father-son bond, whereas others see Tony as Peter’s “cool uncle.” One thing is clear: the two became very close friends over the past few MCU movies. Since Tony recruited Peter to the Avengers, he felt responsible for him.

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This made it all the more tragic when Tony failed to defeat Thanos – the guy whose arrival he’d both been anticipating and fearing for six years – and the most immediate consequence was Peter turning to dust before his eyes. The roles were reversed in Endgame, when Tony sacrificed himself to save the universe and Peter rushed to his side to tell him, “we won, Mr. Stark.”

1. Never quite worked out: Steve Rogers and Tony Stark

Tony talks to Steve in Avengers Endgame

Steve Rogers and Tony Stark never really got along. They were contentious in the first two Avengers movies – Steve thought Tony was all flash and no honor, while Tony resented Steve because his father always talked about how amazing he was – and then any semblance of friendship or mutual respect was shattered in Civil War. Following an intense fight, Steve holds his shield above a helmetless Tony and the look in his eyes tells Tony that Steve is absolutely willing, even for a second, to kill him.

After that, Tony couldn’t bear to call Steve for help in Avengers: Infinity War. They put their differences aside to save the world in Avengers: Endgame, but their friendship couldn’t be salvaged at that point.

NEXT: Avengers: Endgame: 5 Reasons Iron Man Got The Best Ending (& 5 Why Cap Did)