Warning: SPOILERS ahead for Avengers: Endgame

The introduction of "Professor Hulk" in Avengers: Endgame has raised a number of questions among those fans unfamiliar with the original comics, and has also raised some interesting possibilities for the future of Hulk in Phase 4 of the Marvel Cinematic Universe.

Though he's usually depicted as a loner or a monster, the Hulk was a founding member of the Avengers during the Silver Age of American Comics. He was also the first member to quit the team, quickly abandoning the group at the end of Avengers #2 after he discovered that the rest of the Avengers were fearful of him losing control. As such, Hulk's status as a founding Avenger was frequently forgotten in the years before the MCU acknowledged his place as a founder of Earth's Mightiest Heroes.

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When most people think of the Hulk, they generally picture an angry green giant. Yet Bruce Banner's super-strong persona has undergone a great deal of evolution over the years and he has manifested more powerful personalities besides just the Hulk. Some are as smart as Banner himself and others challenge Hulk's assertion that he is "the strongest one there is."

How Bruce Banner and Hulk Combined In Avengers: Endgame

One of the biggest surprises in Avengers: Endgame comes when Steve Rogers, Natasha Romanoff and Scott Lang seek out another genius to help them make Scott's "time heist" plan a reality after Tony Stark dismisses the idea as impossible. Saying that they need a big brain, the action cuts to a diner, where the trio of heroes are pinned into a booth by an articulate Hulk who wears clothes that aren't even ripped (in the subtitled version of Endgame he's credited as "Smart Hulk"). This leads to the revelation that Bruce Banner spent the last five years trying to look at his Hulk persona as "a cure, not a disease" and successfully bringing his two halves into balance, becoming a being with Bruce Banner's intellect and the Hulk's strength.

Though not addressed as such in the movie, this new incarnation of the Hulk was a clear tribute to the Professor Hulk personality from the comics. Created by writer Peter David and artist Dale Keown, Professor Hulk first appeared in Incredible Hulk #377. This issue saw psychiatrist Dr. Leonard Samson working with Bruce Banner to overcome the childhood abuse that gave birth to the various Hulk personas.

The end result was an apparent merging of these personas into what Bruce saw as an idealized being, possessing the best traits of Bruce Banner and the Hulk. It was later revealed that no merging had occurred and that Bruce had simply developed another personality to change into. The Professor Hulk would not be the last new personality Banner would develop.

Related: What Happened To Gamora In Avengers: Endgame?

Bruce Banner Has A Lot More Personalities Than Hulk In The Comics

Before the first appearance of Professor Hulk, Bruce Banner had three confirmed personalities. In addition to his normal self, Banner could transform into the Green Hulk or Savage Hulk. This is the version of the Hulk most people are familiar with, who speaks of himself in the third person ("Hulk Smash!") and has the mental and emotional capacity of a young child. Banner also had a Grey Hulk persona, who lacked the strength of the Savage Hulk but was far more intelligent. Less easily angered than the Savage Hulk, the Grey Hulk was made up of Banner's repressed dark impulses and found employment for a time as an enforcer for the mob in Las Vegas under the name Mr. Fixit.

Many of Banner's other personas are based around the darker aspects of his personality. The Mindless Hulk was created after Doctor Strange's enemy, Nightmare, drew upon Banner's worst fears regarding what he might become and crafted a new Hulk that lacked all of Banner's intelligence and morality. A Devil Hulk was born of Banner's resentment over how he was treated by the world, and threatened to take over Banner's body completely when he was diagnosed with Lou Gehrig's Disease. The Guilt Hulk (a.k.a. The Beast) was born of Banner's guilt over the destruction he had caused as the Hulk and was the largest of Banner's personalities at 20 meters tall.

One persona movie fans are familiar with is the Green Scar. First created by Bruce Banner after he crash landed on the harsh world of Sakaar, this Hulk persona had the strength of the Savage Hulk and intelligence on par with the Grey Hulk. This version of Hulk was adapted for the movie Thor: Ragnarok, which presented a version of Hulk that was smarter and more eloquent than the Hulk seen in previous MCU films but was not as smart as Banner. The comic book version of the Green Scar is also notable for giving rise to the strongest Hulk there is. Known as the World Breaker Hulk, this version of Hulk tapped into the full potential of his rage and was able to defeat the Avengers, the Fantastic Four and the Sentry after fighting without resting over the course of a week.

Perhaps the most dangerous incarnation of the Hulk is the one called the Maestro. Ruler of a future timeline devastated by nuclear war, the radioactive fallout only served to make this version of the Hulk even stronger. Able to lift twice as much in a calm state as a fully enraged Savage Hulk, the Maestro had all of Bruce Banner's intelligence but none of his ethics.

Related: Is Hulk Strong Enough To Defeat Thanos In The MCU?

Other Hulk Personalities The MCU Should Use

The plans for Bruce Banner and Hulk in the MCU heading into Phase 4 are unclear. While Mark Ruffalo is under contract for two more movies, it seems unlikely that Disney will want to pursue a solo Hulk movie since the distribution rights are currently held by Universal Studios and accommodations would have to be made one way or the other. Given that Marvel Studios already have their hands full with the various properties recently reacquired as a result of Disney's purchasing 20th Century Fox, a Hulk solo movie might not be as big a priority as introducing the X-Men or Fantastic Four into the MCU.

One interesting possibility is that Marvel Studios could make a movie based around the various dark  futures of the Marvel Comics' universe as a vehicle for the Maestro. Certainly Marvel has published enough comics based around the Old Man Logan concept for there to be enough heroes to form a post-apocalyptic Avengers team. Just imagine a team-up between elderly versions of Wolverine, Hawkeye and Starlord to save the Earth from an invincible Hulk!

A less dour possibility would be including Hulk's Mr. Fixit persona in Ant-Man 3. Imagine the hilarity of Scott Lang and his ex-con buddies teaming with a few other superheroes to pull off a microscopic heist at the corrupt casino that employs Mr. Fixit as their head of security. True, explaining away how Professor Hulk degenerates into Mr. Fixit would take some doing, but it wouldn't be any stranger than explaining how Banner became Professor Hulk in the first place in Avengers: Endgame. In any case, it will be interesting to see what the future holds in store for Banner and the Incredible Hulk.

More: Avengers: Endgame's Ending & Marvel Movie Future Explained In Detail

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