How can Marvel Comics copyright the common word "Hulk"?

For a long time (most of his career) Hulk Hogan and any organization he wrestled for had to license the word Hulk for him to use it. I think Marvel pulled a fast one on Hulk Hogan. I see them having a claim to "The Incredible Hulk" but Hulk by itself, as in Hulk Hogan, should have been beyond their reach. Hulk Hogan recently bought outright any use to the name Hulk Hogan but I think he was taken and probably could have won in court. Did Marvel cheat or can they legally hold a trademark or copyright on the word "Hulk" in a non-comic book superhero setting? Any lawyer or copyright expert please answer