Abebe Bikila won the gold medal in the marathon at the 1960 Rome Olympics running barefoot.
He was a late inclusion to the team from Ethiopia competing at the Rome Olympics and the team had run out of enough kit for them to have running shoes that fitted him. He did reportedly buy another pair that gave him blisters. Rather than wear an ill-fitting pair of running shoes, he decided to run without any running shoes. The rest is history. He did go on to win the marathon at the next Olympics in 1964 in Tokyo, this time he decided to wear running shoes.