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.
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.
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.