The Incredible Hulk of the Marvel Cinematic Universe has been through a lot. After spending years on the run, afraid of "the other guy," Bruce Banner finally found a family in the Avengers. However, after being partially responsible for the destruction caused by Ultron, he exiled himself to Sakaar in Thor: Ragnarok, only to return to Earth two years later to fight a losing battle against Thanos in Avengers: Infinity War.
In the five years after the blip, Banner found peace in himself, creating the Professor Hulk persona. His peace didn't last, though, as he was once again forced to face tragedy when he lost not only his best friend, Tony Stark, but also former romantic interest Natasha Romanoff. Banner was left hurt and raw after the events of Avengers: Endgame, not just mentally but physically, as last we saw him he still recovering from using the Infinity Stones to undo the blip.
With his three-movie story arc concluded, what could be next for the Green Goliath? The answer might just be... to turn him grey.
The Grey Hulk first appeared in 1962 in The Incredible Hulk #1 by Stan Lee, Jack Kirby and Paul Reinman. Initially, Banner would turn into the Hulk at night and revert back at dawn. This original iteration of the character was meant to represent all of the dark and violent thoughts and impulses of Banner. A fairly shameless ripoff of Dr. Jekyll and Mr. Hyde, he would only come out at night so he could hide his shame in the cover of darkness.
Eventually, due to a color problem in the printing process, Stan Lee would choose to change the Hulk from Grey to Green. This change was explained in-universe as being the result of further gamma mutation, also explaining why Banner would transform due to anger and stress rather than nightfall. Eventually the Grey Hulk would be established as an alternate personality of Banner's, much like the classic green, also known as Savage Hulk. The two Hulks battled for control inside Banner's psyche.
The Grey Hulk is the midway point between the Savage and Professor Hulks. He's smart enough to speak in full sentences but doesn't maintain Banner's subdued, heroic personality. The Grey Hulk is arrogant and manipulative: he represents a side of Banner that he was always afraid to act on. He is also more human than the Savage Hulk, not only in speech, but also control and movement. He doesn't have the same animalistic behavior as the Savage Hulk, nor does he have the same limitless strength.
In the comics, after the Grey Hulk made his return in The Incredible Hulk #324, he took on the persona of Joe Fixit. Calling himself Mr. Fixit, he was a mob enforcer in Las Vegas, wearing a suit and tie. He even had a love life during this time, but eventually Banner regained control. Occasionally, Grey Hulk would convince Banner to bring him out instead of the Savage Hulk, but he largely buried that side of himself once again.
Most recently, Fixit's personality has reemerged again in The Immortal Hulk comics. This version of Fixit is more ruthless and violent than he ever was before. It's unlikely we'll see this cruel version of the Grey Hulk in the MCU, but it still could be a sign that they are bringing him back into the forefront.
Bruce Banner in the MCU has always been an internally conflicted character, but prior to Avengers: Endgame that hadn't fully manifested through the Hulk. While we're told Banner confronted his Hulk persona directly, eventually coming to terms with him and creating the Professor Hulk, it's never shown. The literal battle for control inside Banner's mind is a major part of the character in the comics, and introducing the Grey Hulk is the perfect way to finally portray this aspect.
We've seen the Savage Hulk take on some of the Grey Hulk's traits. In Ragnarok, the Hulk was able to speak in mostly full sentences after spending two years in that form. But he still lacked the cunning of Grey Hulk and maintained a child-like intelligence and attitude. This persona fit the Hulk at that stage in his development, but now that Banner has had to live through the blip as well as the loss of Black Widow, there may be a much darker side of him waiting to release.
Post-Avengers: Endgame, Banner could be a lot more calloused to the world, becoming more reclusive and unfeeling. We've seen Banner attempt to control his dark side in his first three MCU appearances: The Incredible Hulk, The Avengers, and Avengers: Age of Ultron. We've also seen Banner make peace with his dark side in his most recent appearances: Thor: Ragnarok, Avengers: Infinity War, and Avengers: Endgame.
What we haven't seen is a Banner that truly lashes out and gives into his darkness. Finally getting the Grey Hulk in the MCU, ideally in the form of Joe Fixit, would be the ideal next step for his character as he deals with the fallout of the Avengers: Endgame.
With the Hulk's solo film rights still tied up with Universal it's unlikely we'll get to see Banner lead his own film. However, with the recently announced She-Hulk series coming to Disney+, it's clear that Marvel Studios is not done with the character. While there's no guarantee that the She-Hulk series will maintain the origin from the comics tied directly tied to Bruce Banner, it does seem unlikely that the series would neglect to reference or even include Banner at all.
While the upcoming Disney+ shows are reported to have feature film budgets, it still would be a lot to translate the high-stakes action of the cinematic Savage Hulk onto the small screen. Therefore, it makes even more sense to include Banner in She-Hulk as Joe Fixit. With his reduced power and more ground-level stories, he'd make a much better fit for the streaming platform than the Savage or even Professor variations. Also, considering the She-Hulk, Jennifer Walters, is a lawyer by day, it would be a good fit to have her contend with Fixit and his mob ties.
The Grey Hulk may be a new prospect for the MCU, but Marvel has considered using him before in Avengers: Age of Ultron. With his recent reappearance in the comics, it's clear that Marvel has him on their mind. So, while we may not be getting a new Hulk film anytime soon, we may just get Grey Hulk on Disney+ or as a guest in another film in the upcoming Phase 4.