Canelo's major fights were never billed as "Mayweather-Alvarez" or "Cotto-Alvarez." Nobody really refers to him as Saul or Alvarez. I bet casual fans don't realize that Saul is his actual name. I can't remember any other fighter that was like that. Maybe in MMA, where Quinton "Rampage" Jackson's fights used the name "Rampage" instead of Quinton.
Rocky Marciano is the main one I can think of. You NEVER hear anybody refer to him as Rocco. I guess you could say his fight nickname was the Brockton Blockbuster but still, Rocky stuck more than his actual name so I guess it fits the question.
Razor Ruddock too, on a lesser scale.
EDIT: Jersey Joe Walcot, Sugar Ray Robinson...Two names that I know of that aren't even along the lines of the actual birth name of the fighter but live on in their recognition.
I can proudly say that i am one of the chosen few that call him by his name, Saul Alvarez, check the latest thread i did on him.
Anyway, Javier Hernandez is not a fighter but he is also marketed through his nickname "Chicharito" on his sport wich is fútbol..
Personally i would much rather have people know me by my real name but hey its ok to be called names if its gonna make you some gwap i guess, son.