In the 1968 Olympics in Mexico City, Tanzanian runner John Stephen Ahkwari was the last runner in the marathon.
He came in about an hour and a half after the winner, practically carrying his leg, as it was so bloodied and bandaged.
When asked, “Why did you keep going?” He said, “You don’t understand. My country did not send me 5,000 miles to start a race; they sent me to finish it.” (http://speedendurance.com/2007/07/15/how-to-finish-a-marathon-1968-olympics-in-mexico-city/)