Eriksen was born on 8 September 1922 in Kristiania (now
Oslo) in Norway. His father, also called
Marius Eriksen, was a gymnast who competed for Norway at the
1912 Summer Olympics. His mother was Birgit Eriksen. During his early years, Eriksen (junior) gained some success at slalom skiing and ski jumping. Eriksen's younger brother,
Stein Eriksen, went on to win an Olympic gold medal in skiing. Following the outbreak of
World War II, Eriksen fled Norway, leaving on 5 November 1940 via
Ålesund. After arriving in
Scotland, he made his way to
Canada, where he underwent flying training at
Little Norway, the
Norwegian Army Air Service flight training school. On his return to the
United Kingdom, Eriksen served with
No. 331 (Norwegian) Squadron RAF and then
No. 332 (Norwegian) Squadron RAF as a fighter pilot flying
Spitfires. He achieved nine kills, making him one of
Norway's aces, before he was shot down off the coast of the
Netherlands attempting a head-on attack against a
Focke-Wulf Fw 190. Eriksen survived and after being captured on 2 May 1943, he was held as a
prisoner of war at
Stalag Luft III in
Poland until 1945. He began his service with the RAF as a Sergeant, but was later commissioned as a
Second Lieutenant. In recognition of his wartime service, Eriksen was awarded the
War Cross with Sword,
St. Olav's Medal With Oak Branch,
Haakon VIIs 70th Anniversary Medal, the
Norwegian War Medal, the
Norwegian Defence Medal, the British
Distinguished Flying Medal, ==Honours and awards==