I googled "Top 10 NFL running back all-time" and went with the 1st one that they had. Earl Campbell (or however his name is spelled) was #10. I'm sure there are many that would qualify for this list. I'm kinda surprised nobody has picked Sweetness.
Would anyone believe that Gale Sayers had an older brother named Roger who was faster than he was? Roger was a world class sprinter one of the very few to beat Bullet Bob Hayes. Roger was also a great college footballer, only 165 pounds however so there went the NFL.