Before Muhammad Ali, there was an 18 year old named Cassius Clay (178 lbs) that entered the Light Heavyweight division of the 1960 Rome Olympics. Clay went 5-0 on his way to winning gold.
He received a first round bye, and then went on to win his next fight due to a referee stoppage in the 2nd round. He would then finish off his last three fights with convincing unanimous decisions.
The gold medal fight was against Poland’s Zbigniew Pietrzykowski, who was making a return trip to the Olympics after winning bronze in Melbourne 1956.