Here, we will delve into who Red Hulk is both in the movie and in the comics, the difference between the origins and the possible future of the character. We will also cover the characters that didn’t show up, and why their absence is felt once the movie is over.
Spoilers For The Movie Ahead!
Who Is Red Hulk?

The real identity of Red Hulk is General Thaddeus Ross, a high-ranking U.S. military officer who has appeared several times in the MCU. His first appearance was in The Incredible Hulk, released in 2008 and portrayed by the late William Hurt, where he hunted Bruce Banner during his first canonical outing.
General Ross would later appear in several MCU movies playing minor roles, particularly as the voice of the government that tries to regulate the Avengers back in Captain America: Civil War. He comes back in Captain America: Brave New World as the recently elected president of the U.S., this time portrayed by Harrison Ford.
Transforming Into The Red Hulk

The character of Thaddeus Ross is kept mostly unchanged from his comic book counterpart, but the details surrounding his transformation differ greatly. In both cases, the character known as The Leader is involved, but in the movies General Ross is not a willing subject.
In the comics, The Leader (alongside other brilliant Marvel villains) convinces Ross that the only way to defeat Hulk is to gain similar powers, and as such the General becomes Red Hulk willingly.
In the movie, Samuel Sterns (who uses the moniker of The Leader in the comics) uses his gamma-infused intellect to aid Ross in his political career under the promise of freedom. Predicting that the General wouldn’t keep his promise, Samuel drip-fed gamma radiation to Ross through his heart medicine, and later provokes him into becoming Red Hulk.
Why Isn’t Bruce Banner In The Movie?

A movie with Captain America in the title has only one required character: the titular Captain America. However, the various characters that appear other than Sam Wilson make this film feel less like a Captain America sequel and more like an Incredible Hulk one.
Both Samuel Sterns and Betty Ross are portrayed by their original actors, Tim Blake Nelson and Liv Tyler.
However, the movie isn’t built around Bruce showing up, and there is no reason for him to do so. The only moment where someone as strong as Hulk would be needed was in the final confrontation, but Sam Wilson was able to defeat Red Hulk on his own.