Frank Grillo’s first appeared in Captain America: The Winter Soldier as Brock Rumlow. He was a HYDRA infiltrator working as a S.H.I.E.L.D agent and field commander in STRIKE’s team. A building dropped on Rumlow but he manages to escape. Then he was seen in Captain America: civil war as Crossbones in which he killed himself in a building explosion.
It should’ve been the end of the story for Crossbones, but now there are rumors about him returning to MCU. These rumors starts when MCU Cosmic Jeremy Conrad said that Marvel is considering to bring back Crossbones in some way. He also adds that he is still unsure about Crossbones come back. But if he does, it could be like an alternate universe Crossbones in the movie Doctor Strange in the Multiverse of Madness.
Last Year, Frank Grillo also mentioned that he has a contract to do five more movies for Marvel if they will ever contact him. This means in case Marvel decides to bring Crossbones back he has to appear in the movies because of his contract with them.
His Return In Avengers: Endgame
Frank Grillo already made an unexpected return as Brock Rumlow in Avengers: Endgame. When Iron Man, Ant-Man, Captain America, and Hulk go back in time to 2012 to recover some of the Infinity Stones. He was one of the people who got Scepter out of the Avengers Tower and handed it to Baron Von Strucker, who was a HYDRA scientist.
So, it is unquestionable that Crossbones is one of the best Marvel villains. People might see him in the upcoming movies as his contract is still not over. And his surprising role in the Avengers: Endgame also gave hope to his fans that he can reappear in future Marvel movies. Because of the Multi-verse wide open in Marvel movies, Crossbones timeline may appear.