Professional Gymnast, Olympic Silver Medalist, Olympic Bronze Medalist. He was born as Arthur Martinius Amundsen in Oslo, Norway, to planing worker David Amundsen (1862–1935), and his wife Amanda Amundsen (1863–1932), who was from Sweden and who managed a sewing business, on March 22, 1886. He worked as a merchant and then became active in sports. He was a professional gymnast who was a member of the club Oslo Turnforening of Oslo, Norway. He would eventually go onto represent his home country of Norway at the 1908 Summer Olympics that were held in London, England. Together with his team members including Carl Albert Andersen, Otto Authén, Herman Bohne, Trygve Bøyesen, Oskar Bye, Conrad Carlsrud, Sverre Grøner, Harald Halvorsen, Harald Hansen, Eugen Ingebretsen, Ole Iversen, Per Jespersen, Sigurd Johannessen, Nicolai Kiær, Carl Klæth, Thor Larsen, Rolf Lefdahl, Hans Lem, Anders Moen, Frithjof Olsen, Paul Pedersen, Carl Alfred Pedersen, Sigvard Sivertsen, John Skrataas, Harald Smedvik, Andreas Strand, Olaf Syvertsen, and Thomas Thorstensen, he was part of the Norwegian men's gymnastics team which won an Olympic Silver Medal in the Team All-Around Competition Artistic Gymnastics Men's Event. His final team standing score result was ranking 2 with 425 points. He also competed as a member of the club Oslo Turnforening of Oslo, Norway, four years later at the 1912 Summer Olympics that were held in Stockholm, Sweden. Together with his team members including Jørgen Andersen, Trygve Bøyesen, Georg Brustad, Conrad Christensen, Oscar Engelstad, Marius Eriksen, Aksel Hansen, Eugen Ingebretsen, Olaf Ingebrigtsen, Olaf Jacobsen, Erling Jensen, Thor Jensen, Frithjof Olsen, Oscar Olstad, Edvin Paulsen, Carl Alfred Pedersen, Paul Pedersen, Realf Robach, Sigurd Smebye, and Torleif Torkildsen, he was part of the Norwegian men's gymnastics team which won an Olympic Bronze Medal in the Team All-Around Competition Artistic Gymnastics Swedish System Men's Event. His final team standing score was ranking 3 with 857.21 points. He continued to represent club Oslo Turnforening, of Oslo, Norway, and be active in sports events until his death. He was married to Martha Olefine Andrea Haga Amundsen (1884-1941), with whom he had two children, a daughter, Elsa Amundsen Tollefsen (1912-2010), and a son, Erik Haga Amundsen (1913-1994). He passed away unexpectedly in his native Oslo, Norway, on February 25, 1936, one month before his 50th birthday, and he was buried in Vår Frelsers gravlund (or Cemetery of Our Saviour), in Oslo, Norway, with several other family members including his parents, grandparents, and his wife Martha who passed away six years later on November 11, 1941, at the age of 57, and where several other famous Norwegian personalities are also laid to rest.