Bernard Hopkins was a reigning middleweight champion when this century began and about to turn 35. In September 2001, he beat Felix Trinidad by Round 12 TKO.

In 2004, he knocked out Oscar De La Hoya in Round 9 to become that incredibly rare bird in the modern boxing world: an absolutely, 100 percent undisputed world champion. He united every belt available at middleweight. 

He lost two straight fights to Jermaine Taylor in 2005,when he turned 40. I thought he should have won the fights, but it did seem like he might finally be slowing down. 

Instead of retiring, which seemed like a likely course of action, he jumped to light heavyweight and beat Antonio Tarver to become a two-division world champion. 

At 43, Hopkins lost a split decision to Joe Calzaghe that he deserved to win, in my opinion. But again, it looked like he might have reached the end of his amazing career. 

Instead he came back six months later and a weight class lower. In October 2008, he faced Kelly Pavlik at super middleweight. A lot of boxing writers predicted Pavlik would be the first fighter to knock Hopkins out. 

Instead, the ageless Hopkins beat the tar out of Pavlik. When the decade ended, he was about to turn 45 and still a major player on the boxing scene.