As the current chapter of the Marvel Cinematic Universe comes to a close, we'll likely be saying farewell to a number of classic characters, one of them potentially being the Incredible Hulk, played by Mark Ruffalo. It's difficult to say right now because the actor's contract -- unlike that of fellow stars Robert Downey Jr., Chris Evans and Chris Hemsworth -- does not expire with Avengers: Endgame, meaning he could make an appearance in Phase Four.

Ruffalo has been playing Hulk for about eight years now, and while he hasn't been given a solo film, the Hulk has been explored surprisingly well, enough that we can see how his character-defining inner conflict has developed. With the end of the "Infinity Saga" fast approaching, now seems like a good time for a look back at the raging fire that is the relationship between Bruce Banner and his wrathful alter ego. For the most part, they have always hated each other for their respective weaknesses.

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Marvel Studios didn't bother with a proper origin story for the Hulk, as audiences got one just five years earlier. So, when Bruce Banner (back when he was Edward Norton) first appeared in The Incredible Hulk, he was already living with the gamma-induced monster, hiding somewhere in the favelas of Rio de Janeiro, struggling to find a cure for his predicament.

The film showcased the tragedy of his situation, revealing he had left his life and love behind because of his pursuer, Thaddeus Ross. But the real reason why he could never have those things was, and always has been, the fact that he had to keep the destructive beast at bay. So, even when Ross abandoned his pursuit of the Hulk, Banner fled into isolation, where he attempted to gain control.

Unfortunately, as he revealed to the others in The Avengers, control didn't seem possible, so he sought a more permanent end. That too failed. It seemed he would never be rid of the Hulk, so Banner traveled to India, where he worked as a doctor, trying to do good in his own way and living in fragile unity with Hulk.

Then S.H.I.E.L.D. came along...

When Loki arrived on Earth, threatening to conquer the planet using the Tesseract (which held the Space Stone, unbeknownst to anyone at the time), Nick Fury turned to Earth's Mightiest Heroes. The god of mischief had counted on it, and Hulk was used to wreak havoc on the Helicarrier. However, as much destruction as he had caused, Hulk proved himself to be a worthy defender of Earth in the Battle for New York, capable of listening to orders from Captain America and fighting alongside others like Thor.

None of that made the Hulk as reliable an ally as any of the other members of the newly formed Avengers. Bruce on the other hand, became a trusted friend, as we saw in his brief appearance in Iron Man 3. Stark felt comfortable enough to confide in Bruce while Natasha, by the time of Avengers: Age of Ultron, had developed feelings for him, going so far as to suggest that she felt they were the only ones on the team who could truly understand each other.

Hulk and Black Widow about to touch in in Avengers: Age of Ultron

For a time, Banner and Natasha appeared to have worked out a way of calming the Hulk enough for Banner to return, but like all the other attempts, it did very little to hinder transformations or minimize the burden on Banner's shoulders. He seemed to realize that Hulk wasn't the only one capable of destruction, since it was Bruce -- due to Stark's silver tongue -- that helped create Ultron. After the Hulk threatened to destroy Johannesburg, Banner had had enough. So, when the opportunity to free Earth from his presence arose, he -- in the form of the Hulk -- took it and flew from Sokovia to Sakaar.

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He remained there for two years, trapped in the form of the Hulk. It allowed the powerful creature to develop further, so much so that by the time Thor found him in Thor: Ragnarok, he had developed the ability to speak and talk about abstract concepts. It's how he was able to express the "raging fire" within him.

But that did nothing to change the relationship between Hulk and Bruce. If anything, it made it worse. Banner knew that Hulk had gained more control over the past couple of years and, as he told Thor, "in the past I always felt like Hulk and I each had a hand on the wheel, but this time it's like he had the keys to the car and I was locked in the trunk," warning the God of Thunder that if he turned into the Hulk again, Banner might never come back. Knowing that, he still readily leapt into danger and transformed when Fenris and the rest of Hela's forces threatened to wipe out the Asgardians on the Bifrost, proving that despite everything, Banner was a good man at heart.

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He would get another chance to prove that to himself and everyone else in Avengers: Infinity War (directed by Joe and Anthony Russo).

Following Ragnarok, Thor, Loki, Valkyrie and Banner traveled through space on the Statesman, searching for a new place to call Asgard before they were set upon by Sanctuary II, the colossal warship belonging to Thanos.

The Mad Titan had come for the Space Stone, which lay within the Tesseract. After wiping out half of the Statesman's passengers, Thanos turned to the leaders. Loki, in one last attempt to secure victory, stalled to give Hulk the element of surprise. Even that didn't work. Thanos beat the Hulk easily.

Infinity-War-Bruce-Banner

The Hulk has always been able to destroy his enemies. His strength seemed to stem from the belief that there was nothing in the universe stronger than he was. That changed when he was defeated in a fist fight with Thanos. It scared him, destroyed his very identity and caused him to hide away within the confines of Banner's mind, leaving Banner effectively powerless.

Without the Hulk, Bruce has only ever had his intellect to aid the Avengers. He has never possessed superhuman powers or abilities and yet, throughout Infinity War, he never stood down from the fight. He did everything he could, whether it was simply warning others or donning the Hulkbuster armor to help fight in Wakanda. In the end, it seemed Hulk was wrong about Banner. He might be physically smaller, but Banner himself is not a weak person.

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The relationship between Banner and Hulk might have appeared to be an antagonism of brains and brawn at first, but over the past 10 years it has developed into so much more. They have always hated one another for their weaknesses, but at least they have been able to form a tenuous partnership when necessary. Now that those weaknesses and strengths have come into question, Banner and Hulk may be on the verge of a change for the better.

If the rumors regarding Professor Hulk are true, it seems Avengers: Endgame will give Hulk and Banner a satisfying conclusion to their story, in which they're able to reconcile their differences, embrace and accept each other, thus becoming a powerful force of intellect and strength. If they can achieve that, Banner may find all the things he implied he wanted in Age of Ultron suddenly in reach.

Directed by Anthony and Joe Russo, Avengers: Endgame stars Robert Downey Jr., Chris Evans, Mark Ruffalo, Chris Hemsworth, Scarlett Johansson, Jeremy Renner, Don Cheadle, Paul Rudd, Brie Larson, Karen Gillan, Danai Gurira, Benedict Wong, Jon Favreau and Bradley Cooper, with Gwyneth Paltrow and Josh Brolin. The film arrives April 26.