Roy Jones Jr.
Let’s be real, Jones is considered by most as one of the best boxers of all time, pound for pound. He left his mark in boxing history when he won the WBA heavyweight title in 2003, thus becoming the first former middleweight champion to have won a heavyweight title in 106 years. From 1989 to 2018, Roy competed for titles and is a six-time world champion in four weight classes.
Marvelous Marvin Hagler
Fun fact, at six years and seven months, Marvelous Marvin Hagler reigned as the undisputed middleweight champion, making this the second longest reign of the last century, just behind Tony Zale. Currently, he also holds the highest knockout percentage of all undisputed middleweight champions, at a whopping 78%.