Samuel B. Thomsen (born July 10, 1931, in Saint Paul, Minnesota) is a former career diplomat who was the first United States Ambassador to the Marshall Islands, serving there from 1987 to 1990. Thomsen entered the United States Foreign Service in 1960 and served in various positions in the United States Department of State, and in diplomatic assignments to Vietnam, Laos, Botswana and Nigeria. While serving as Consul at Hue, Thomsen served as a political advisor to the commanding general of the U.S. Marines in Vietnam, Lt. Gen. Lewis Walt, from July 1965 to July 1966. During Thomsen's service in the Marshall Islands, the office of the U.S. Representative was upgraded to Embassy status.