I would say it's something along the lines of:

1. Jim Brown
1A. Walter Payton.

Many forget Brown retired at the height of his career as well. Brown is sort of like Babe Ruth in that he was SO utterly dominate before the NFL really became all the rage and thus, all of his accomplishments get pushed aside because they were set before the rush of popularity.

Payton certainly was one of the most graceful people on and off the field, but I'd argue that Brown was just as important because of what he stood for, as a black player during the civil rights movement.

Take care all.