WARNING: The following article contains major spoilers for Avengers: Endgame, in theaters now.
The long-anticipated Professor Hulk made his Marvel Cinematic Universe debut in Avengers: Endgame, much to the delight of audiences worldwide. As in the source material, after years of push and pull, the two sides of Marvel's Gamma-infused hero have merged into one personality, with the brute strength of the Hulk and the intelligence of Bruce Banner.
As directors Joe and Anthony Russo explained during an appearance at the Smithsonian Institute in Washington, D.C., it was a natural progression for the characters. Following Endgame's opening act, which culminated with the killing of Thanos after he revealed he had destroyed the Infinity Stones to ensure his victory in Avengers: Infinity War would be final, the narrative jumps five years into the future. And while every member of the team has undergone a lot during that time, perhaps the most drastic change is that Banner and the Hulk, at odds for years, have come together as one.
For the Russos, the change served as the culmination of a character arc that began in 2008's The Incredible Hulk, but also stemmed from the guilt carried over by the Hulk and Banner from Infinity War. Joe Russo saw the character as two separate personalities, rather than different sides of one individual. The two hated each other as they warred for possession of the host body.
That conflict resulted in the Hulk refusing to relinquish control of the host body to Banner for more than two years between the events of Avengers: Age of Ultron and Thor: Ragnarok. The dysfunction and animosity between the pair reached its peak in Infinity War, when the Hulk refused to come out to help Banner multiple times over the course of the film, despite facing mortal danger in the form of Thanos and his Black Order.
Following Hulk and Banner's respective defeats against Thanos, and the Mad Titan using the Infinity Gauntlet to wipe out half of all life in the universe, both personalities found themselves carrying an enormous amount of guilt, feeling at least partially responsible because of their inability to work together. Joe Russo noted that in the aftermath of Thanos' death and the destruction of the Infinity Stones, Banner and Hulk finally came to a compromise. As a result, they're now merged into one as Professor Hulk, a significant moment of personal growth and reconciliation between the two.
Anthony Russo observed that Hulk's arc is representative of how he and his brother approached directing their MCU films: Focus on the characters rather than increased spectacle. Given the nature of the stories and characters involved, the spectacle will naturally present itself, but the emotional investment is what will ultimately keep the audience returning.
Directed by Joe and Anthony Russo, Avengers: Endgame stars Robert Downey Jr. as Iron Man, Chris Evans as Captain America, Mark Ruffalo as Bruce Banner, Chris Hemsworth as Thor, Scarlett Johansson as Black Widow, Jeremy Renner as Hawkeye, Brie Larson as Captain Marvel, Paul Rudd as Ant-Man, Don Cheadle as War Machine, Karen Gillan as Nebula, Danai Gurira as Okoye and Bradley Cooper as Rocket, with Gwyneth Paltrow Pepper Potts, Jon Favreau as Happy Hogan, Benedict Wong as Wong, Tessa Thompson as Valkyrie and Josh Brolin as Thanos.