William Nicholas Leonard (January 12, 1916 – August 21, 2005) was an American World War II flying ace and rear admiral in the United States Navy. He was born in Douglas, Arizona, the son of United States Army Colonel Charles F. and Hannah M. Leonard. "In the words of Barrett Tillman, WWII aviation historian, [Leonard] is a 'national treasure' because he is so generous with his time and knowledge, records, and photos." After the war, he became a test pilot and commander, including of carrier groups. He retired in 1971 as a rear admiral.