Oscar Olsen represented the Milwaukee AC on the winning tug-of-war team in 1904. Like all the members of that team, he was actually from Chicago. There was a team event in the 1904 Olympic athletics (track & field) competition, with the Milwaukee AC, a contender for the team title. The club convinced several Chicago athletes, including Olsen, to compete for them in tug-of-war, which was considered an event in track & field in that era. Olsen also placed fourth in the two-handed weightlifting event at the 1904 Olympics.
Born in Oslo, Norway, Olsen came to the United States as a youth in the early 1880s. He was a longtime member of the Sleipner Athletic Club in Chicago, also known as the Norwegian-American Athletic Association. Alongside fellow 1904 competitor Conrad Magnusson, he was a member of the highly successful Sleipner AC the tug-of-war team which won multiple state and national championship titles in the 1900s. By profession, Olsen was a machinist for a printing press company. He was naturalized as an American citizen in 1942, and remained in Chicago until his death in 1962 at the age of 86.