Oscar Littleton Chapman (October 22, 1896 February 8, 1978) was the United States Secretary of the Interior during the last three years of the Truman administration. Chapman was born in Omega, Virginia. He attended the University of Denver, where he earned his LL.D. at Westminster Law School, and the University of New Mexico. From 1918 to 1920, Chapman served in the United States Navy Medical Corps. Chapman was the manager of Edward P. Costigan's U.S. Senate campaign in 1930, and the Alva B. Adams Senate campaign in 1932. After Roosevelt's election in 1932, he was appointed as an Assistant Secretary in the Department of the Interior.