Rear Admiral Reginald Fairfax Nicholson (15 December 1852 – 19 December 1939) was an officer in the United States Navy. He fought in the American Civil War and Spanish-American War, was Commander-in-Chief of the United States Asiatic Fleet, and came out of retirement during World War I to serve as the first U.S. naval attaché to Ecuador and Peru. He retired as the last active-duty U.S. Navy officer to have served in the American Civil War.