Though it's exceedingly rare, Mayweather is not the first to go undefeated. Surprisingly, the majority of fighters who retired with a perfect record aren't all that highly regarded.
The list would be significantly better if it included Ricardo Lopez, the great Mexican champion who retired with a 51-0-1 record and 38 knockouts. Only a 1998 draw with Rosendo Alvarez in a title unification bout kept Lopez from being perfect.
Of those who ended their careers with no losses and no draws, the best, and by far the most well known, is the great heavyweight champion Rocky Marciano. The "Brockton Blockbuster" retired at his peak at age 32 in 1955 with a 49-0 record and 43 knockouts.
Marciano scored wins over legends like Archie Moore, Ezzard Charles, Joe Walcott and the great Joe Louis.
Super middleweight Joe Calzaghe retired in 2009 with a 46-0 and 32 knockouts, finishing his career with wins over veteran Bernard Hopkins and Roy Jones Jr. in 2008.
The late Edwin Valero, who died in jail in 2010, had the most perfect record of any fighter ever. Valero was 27-0 with 27 knockouts, including 19 in the first round and two more in the second round.
Veteran Harry Simon, who held super welterweight and middleweight titles, remains somewhat active at 41 with a 27-0 record and 20 knockouts. He didn't fight at all from 2003 through 2006. He fought once in 2007, twice in 2010 and most recently fought in June.
Though Simon was a quality fighter in his day, with wins over Winky Wright and Hacine Cherifi, among others, he is hardly considered an all-time great. Nor is Sven Ottke, who retired in 2004 with a 34-0 record and six knockouts.
There have been others, none of whom is regarded by boxing historians as exceptional.
When boxing cognoscenti speak of the greatest fighters of all-time, the names that often come up are Sugar Ray Robinson and Henry Armstrong. Robinson lost 19 times and Armstrong dropped 21, but there aren't any fighters remotely close to them in the all-time ratings.
If Mayweather does finish unbeaten – and given the few number of bouts he has left, that's likely – he'll vie with Marciano and Calzaghe for the honour of the greatest unbeaten, untied fighter in boxing history.
Nothing he might possibly do in the remainder of his career, though, could help Mayweather to remotely challenge Robinson or Armstrong for their spots as the all-time greatest fighters.
With that, here are the latest Yahoo! Sports boxing top 10 rankings:
1. Floyd Mayweather Jr.
2. Andre Ward
3. Manny Pacquiao
4. Sergio Martinez
6. Juan Manuel Marquez
5. Nonito Donaire Jr.
7. Wladimir Klitschko
8. Timothy Bradley
9. Vitali Klitschko
10. Carl Froch
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- Rocky Marciano