What is a "great" nickname ?
In my view, it's a name or a word that best and most succinctly describes the style or persona of a great fighter.
"El Terrible" Morales
"Big" George Foreman
"Smokin" Joe
Thomas "The Hitman" Hearns
"Iron" Mike Tyson
^these all are great nicknames for great fighters.
The absolute best though is *indubitably (to quote a word from that troll haired freak, Don King) is "Sugar" Ray Robinson.
That nickname transcended boxing into the wider world. It skipped time and generations and even other sports.
A close second, like 1b to a 1a is my man Ali's.
The Greatest or The G.O.A.T
The only reason I place Sugar above it is because while there has been many Sugars, there's only ever been one G.O.A.T (RIP).