Warning: This article contains spoilers for Avengers: Endgame, in theaters now.
By any standard, the Hulk is one of the strongest, most durable beings in the Marvel Universe. And in Avengers: Endgame, the Hulk combined Bruce Banner's brains with his considerable brawn as the Smart Hulk. However, none of that makes Mark Ruffalo's Avenger invincible.
After using the full power of the Infinity Stones and Tony Stark's Infinity Gauntlet to revive all of Thanos' victims in Endgame, the Hulk sustained massive injuries to his right arm.
In an interview with ComicBook.com, Endgame co-director Joe Russo confirmed that the Hulk's arm was permanently damaged.
"He's lost an arm…that's not coming back," Russo said. "He's damaged himself. It's permanent damage, the same way there was permanent damage with Thanos. It's irreversible."
Unlike its comic book counterpart, the Marvel Cinematic Universe's Infinity Gauntlet takes a massive toll on whoever wields it. As Endgame confirmed, Thanos' arm was permanently disfigured after he used the Infinity Gauntlet to wipe out half of all life in the universe in Avengers: Infinity War, and the Gauntlet's energies killed Tony Stark after he used it to defeat Thanos.
When the Hulk used the Stark Gauntlet to undo Thanos' actions, his arm was severely disfigured, even though he received immediate medical treatment.
"As you may notice, his arm is skinnier, it's blackened," Russo said. "So he loses a lot of strength there."
After he used the Gauntlet, the Hulk remained in a cast for the duration of the movie, including through the final battle and to Stark's funeral.
Despite the apparent finality of everything involving the Infinity Stones, Russo said that there could still be a way for the Hulk to regain his lost strength.
"Who knows? There's a lot of really smart people left," Russo said. "Maybe somebody helps him repair that. Maybe somebody gives him a new arm. Who knows? I have no idea where that character goes from here.
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. The film is in theaters now.