Historical clue formulations

• Sports Illustrated named him "Sportsman of the Century" in 1999 — 2020-05-31
• Who said "My only fault is that I don't realize how great I really am" — 2015-04-10
• "It's hard to be humble when you're as great as I am" speaker — 2011-10-31
• Self-proclaimed "astronaut of boxing" — 2010-08-24