Bruce Banner is absolutely key to Avengers: Endgame as the Hulk has multiple moments where he helps the team recover the lives lost to the Decimation. In a recent Reddit AMA, the film's directors Joe and Anthony Russo answered a fan question about possible changes to Hulk's storyline in Avengers: Endgame. The Russo brothers held fast to the idea that Bruce Banner would always be the one to perform the second snap that brought the calvary in for the final act of the film.
A lot is made early in the film about Hulk being destined to wear the Stark Gauntlet once all the Infinity Stones were assembled from their respective time periods. Because Banner's powers stem from Gamma radiation, the Hulk is uniquely suited to weild the fearsome power of the gauntlet without it putting him in mortal danger. His efforts as a scientist also prove key in gathering the stones from their hiding places and putting them back after the fight is over.
We’re Joe and Anthony Russo, directors of Marvel Studios’ Avengers: Endgame. AMA! from r/marvelstudios
Banner's meeting with the Ancient One during the battle of New York also serves as a lynchpin of Avengers: Endgame because of how that conversation forecasts everything coming in the last third. On the commentary track for the film, writers Christopher Markus and Stephen McFeely and directors Joe and Anthony Russo break down why this conversation needed to happen.
"Another scene that took a lot of rejiggering and jiggering," said Markus. "To make things complicated things clear and clear enough so that people could track why certain decisions are made later."
"And that if this is how, why she is, that if Strange were to give that stone away willingly, that there would be purpose behind that action, and that perhaps the purpose of that action was for her in this moment," Joe Russo added. "This scene paints the stakes for motivating Cap to return at the end of the movie."
This exchange turns Avengers: Endgame from a one-way time heist back into a cyclical affair reflecting how Tony Stark's model of time looked when he solved the riddle of time travel. Everything must go back where it came from or more poetically, "Everything will go exactly how it is supposed to."
There were other choices the filmmakers left behind during the creative process. The red-skinned iteration of Hulk was once briefly considered for Avengers: Endgame, according to co-writer Christopher Markus.
“I entertained the idea for about a day,” Markus told Backstory Magazine when asked if Smart Hulk’s (Mark Ruffalo) fleeting red-tinged glow, caused by exposure to the cosmic energies of the six Infinity Stones when performing a snap, indicated Markus and co-writer Stephen McFeely entertained the idea of Red Hulk.
Even though his final story had many twists and turns, there is no way for the Avengers to save the world without the Hulk’s brains. Who knows what changes lie ahead for the character in Phase 4 and beyond.