Quote Originally Posted by The Rookie Fan
It is a very hard thing to do. Think it has only been done twice in history. (I'm not counting Sven Otkey)

And the guys who did it only fought in one weight class. For a multidivision champion to retire undefeated would truelly be amazing. But I believe the money and the fame will keep bringing him back till he either looses or comes very close to loosing.

Don't know who will do it though.
4 have retired undefeated as champions Sven Ottke, Ji Won Kim, Ricardo Lopez, Rocky Marciano. And as for the question in this thread yes Mayweather will retire undefeated.