With over 20 movies and a brand new TV show, the MCU has come a very long way from where it began. One character that has changed almost entirely is Bruce Banner. His journey from a wandering scientist to the savior of humanity has been a sight to behold. However, one theory suggests that before he snapped his fingers, Banner had solved another great mystery.
Years before Endgame, the MCU was trying to figure out the secret to Professor Erskine's Super Soldier Serum -- the same one that created both Captain America and the Red Skull. One Reddit user has proposed a theory that Dr. Banner had solved the formula in The Incredible Hulk. The theory relies heavily on what the Serum bolsters mentally, rather than physically.
In Captain America: The First Avenger, Erskine tells Steve Rogers that the Serum he designed would grant amazing physical abilities and strengthen the person's core values. For Steve, he was a selfless person, and that kindness only grew with the serum. For the Red Skull, he was filled with a desire for power and harbored hate. As expected, this only grew along with his strength. In Banner's case, he carried with him immense rage that had been suppressed for years. His version of the serum bolstered that rage in the Hulk.
The theory begins to carry more weight the moment Blonsky takes the experimental serum. His physical attributes are enhanced, but so is his desire for more power. That greed would eventually lead him to become the Abomination. Many Reddit users agreed with this theory and even began to propose their own additional theories. In particular, one user posited that the Super Soldier Serum was in itself an attempt to replicate the effects of the Black Panther's Heart-Shaped Herb. It was suggested that perhaps someone saw a Black Panther in action and attempted to bring that science to Nazi Germany.
Another theory was brought in regarding the change in the procedure to create the Hulk as opposed to how Steve became Captain America. For Steve, the main factor that helped his cells adapt to the serum was the inclusion of Vita-Rays -- a form of radiation that hasn't been seen since his creation. Banner substituted Vita-Rays for Gamma Rays in his experiment, which could have been why the Hulk was born. The intensity of the radiation manifested the strength and rage of Bruce Banner into the Hulk while Banner remained the same.
The theory itself holds a lot of water and appears to be on the cusp of a pretty exciting revelation should Marvel ever decide to pull on that thread again. With Abomination returning in She-Hulk, there is a possibility that the MCU will dig deeper into gamma experimentation and explore how Erskine's serum played a role in that. It is also interesting to note that Banner had no idea that he was working on a new serum. Instead, he believed he was working on keeping soldiers safe from radiation, hence the gamma.
While not as appreciated as most of the other films, The Incredible Hulk put forth many ideas and characters that continue to play important roles in the larger MCU. Tying Captain America to the Hulk in terms of origin would be an amazing connective tissue for the overall franchise. With more and more movies connecting to past releases, like Shang-Chi and the Legend of the Ten Rings, it makes certain theories feel more plausible than ever.