LAS VEGAS -- One of only two fighters ever to hold UFC championships in multiple weight classes can now add another credential to his resume: Hall of Famer.
The 36-year-old from Hilo, Hawaii became a fan favorite for his willingness to fight anyone. This paid off in one of the legendary upsets in MMA history, when the lightweight Penn went up to welterweight and submitted fellow Hall of Famer Matt Hughes to claim the UFC welterweight belt at UFC 46 in Las Vegas on Jan. 31, 2004. That was Hughes' only loss during a 20-fight run in his prime.
Penn added his second title four years later, when he submitted Joe Stevenson to claim the vacant UFC lightweight title at UFC 80 in Newcastle, England, in Jan. 2008. He solidified his claim by finishing former champ Sean Sherk, who had been stripped of the title, at UFC 84.
The fighter nicknamed "The Prodigy" finished with a record of 16-10-2, but that record doesn't do justice to Penn's fighting spirit. He once fought, and went the distance, with future UFC light heavyweight champion Lyoto Machida; Penn weight 192 for the bout and Machida 225. Penn even issued a challenge to then-UFC heavyweight champion Tim Sylvia back in 2006, though that one went unfulfilled.
As lightweight champion, Penn went up and challenged Georges St-Pierre for the latter's welterweight belt at UFC 94, which did an estimated 920,000 pay-per-view buys. The Jan. 31, 2009 fight, won by St-Pierre when Penn's corner stopped the fight at the end of the fourth round, remains the last time two reigning UFC champions have squared off.
Penn went 1-5-1 over his last seven bouts, with three of those losses to Frankie Edgar. He bounced from lightweight to welterweight and all the way down to featherweight trying to regain his mojo. His last career victory was at UFC 123, a 21-second KO of Hughes to claim victory in their trilogy. He announced his retirement in an emotional post-fight press conference following his final loss to Edgar last July.