Charles Albert Varnum (June 21, 1849 – February 26, 1936) was a career United States Army officer. He was most noted as the commander of the scouts for George Armstrong Custer in the Little Bighorn Campaign (of which he was the last of the surviving officers to die of natural causes) during the Great Sioux War, as well as receiving the Medal of Honor for his actions in a conflict at Drexel Mission following the Wounded Knee Massacre.