Colin Riley McMillan (July 27, 1935 – July 24, 2003) was an Assistant United States Secretary of Defense under President George H. W. Bush during the Gulf War. He was awaiting confirmation as United States Secretary of the Navy in 2003 when he died from an apparently gunshot wound in the head at his New Mexico ranch. McMillan earned his bachelor's degree from the University of North Carolina in 1957. He served in the United States Marine Corps from 1957 to 1960 and in the Marine Corps Reserve from 1960 to 1972.