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Before George Foreman knocked out Joe Frazier to become the heavyweight champion or fought Muhammad Ali in one of the most memorable fights ever ... Big George won Olympic gold in 1968 -- and now the medal's on the block!!

Foreman, who was just 19, was dominant in Mexico City, steamrolling his opps on the way to winning the '68 Summer Games.

George's toughest challenge came in his first fight against Poland's Lucjan Trela -- in the round of 16 -- a bout he won 4-1. Getty

From there, it was easy work for Foreman. He badly hurt Ion Alexe from Romania in the quarterfinals, forcing the referee to stop the contest in the third.

In the semifinals, Big George put Italy's Giorgio Bambini on his ass three times, winning by second-round knockout.

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