How famous are boxers?

if you ask anyone who mike tyson or muhammad ali is, they will know. now i thought floyd mayweather was famous but i went around asking random people at school if they knew who he was, they said no, while saying yes to tyson and ali. how come tyson and ali are so famous. i know they were great in the sport but so were guys like sugar ray robinson and ray leonard but if i ask people if they know those guys they have no clue as to who im talking about.