Clarence Harrison DeMar was a U.S. marathoner, winner of seven Boston Marathons, and Bronze medalist at the 1924 Paris Olympics. He was known by the nickname "Mr. DeMarathon."
DeMar was born in Madeira, Ohio. The 1910 Boston marathon was DeMar's first; he finished 2nd. Later in 1910 he was advised by a doctor that he had a heart murmur and should stop running within a year or two. The next year at the Boston marathon the doctors on the starting line advised him of his heart murmur and told him that he should drop out if he was fatigued, and that he should not run any more races. Nevertheless, he won in 2:21:39, a course record. DeMar was one of the twelve members of the U.S. marathon team in the 1912 Summer Olympics, where he ran poorly, finishing 12th, complaining that the coaching staff's dictatorial control over the athletes' training had harmed the team's performance.
Although DeMar ran a few races after the Olympics, he soon took a break from serious competition. In his autobiography, he gave his reasons as continuing warnings from doctors that he was endangering his health, concern that striving for individual athletic glory was incompatible with the spirit of his religion, and demands on his time from the University extension courses that he was taking at Harvard and Boston University. In June 1915 DeMar received an Associate of Arts degree from Harvard while working as a printer in the Boston area.