5. Henry Armstrong
Homicide Hank, the only fighter to simultaneously hold world titles at three separate weights, has already featured in our welter countdown.
But it was at featherweight where Armstrong, a ring whirling dervish, forged his greatness.
He beat Petey Sarron for the undisputed crown in October, 1937, but never defended the title, electing to move on to bigger things and bigger opponents.
Quite simply, Armstrong was a marvel between the ropes.