Kristoffer Olsen came from an old family of sailors. He was initially an office manager at the firm Ejnar Stensrud & Skien. In 1915, Olsen established the shipping company Olsen & Ugelstad together with his friend Rudolf Ugelstad. The company grew rapidly due to the loss of tonnage during World War I and the demand for transport capacity for the growing oil trade. In Oslo, Olsen was a member of the city council 1927-31 and a number of occupational associations. In 1942, he was detained for four months by the former fascist Quisling government in Norway. After his death, there were decades of litigation concerning his large estate.