Sonic is the most obvious one for me but everyone already can guess why. So I won't go into details.
I feel Cervantes was one of the best final (sub-final) bosses in fighting game history. His moves just oozed with confidence and Namco nailed the idea of a possessed pirate (given that its a 1996 fighting game). I'm not going to claim that he was revolutionary or anything- he was just a cool character. When looking back at him just rememer that this is from the mid 90s- so take his presence with a grain of salt.
But the series after that obviously had Nightmare replace him as the main antagonist (Inferno- for the record- is fucking garbage and was probably designed in about an hour). Nightmare was alight, but he was just a brute in comparison to Cervantes. Meanwhile Cervantes just became more and more of stereotypical pirate like something out of a damn Disney film. He also screamed randomly which was unintentionally funny. Bad voice acting didn't help either. "NOOOO MERRRRCEEE" He got progressively worse from there. I stopped caring about the franchise with the release of IV which might as well have been a Star Wars game.