Ralph Stover Keyser (May 10, 1883 – April 19, 1955) was a highly decorated officer of the United States of America with the rank of major general, who is most noted for his service as the 15th Assistant to the Major General Commandant of the Marine Corps and a distinguished marksman, who participated in world matches. He was the recipient of Navy Cross, the United States military's second-highest decoration awarded for valor in combat.

Ralph S. Keyser was born May 10, 1883, in Thoroughfare, Virginia, as a son of Charles Eugene and Mary Gill Stover Keyser. He enlisted in the United States Army in 1902 and participated in the Philippine–American War. He applied for Marine Corps commission during 1905 and was subsequently commissioned second lieutenant on March 29, 1905. Keyser was subsequently ordered to the School of Application at Annapolis, Maryland, for further officer training, which he completed in April 1906. Among his classmates at that time, were his lifelong friends Holland M. Smith, Andrew B. Drum and Maurice E. Shearer.

Following the school, he was attached to the Marine detachment aboard the newly commissioned battleship USS Louisiana and sailed to Cuba in order to suppress armed revolt of independence war veterans who defeated the meager government forces. Louisiana was then stationed in the Caribbean during the construction of Panama Canal and joined Great White Fleet in December 1907. While aboard the Louisiana, Keyser took part in the voyage around the world with the stops in Port of Spain, Rio de Janeiro, Punta Arenas, Melbourne, Sydney, Auckland, Manila, Yokohama, Singapore, entering the Indian Ocean in December 1908; they coaled in Colombo and passed through the Suez Canal with another stops in Port Said, Gibraltar, and finally returned to Hampton Roads on 22 February 1909.

Keyser was detached from Louisiana in April 1909 and promoted to the rank of first lieutenant one month later. He was subsequently ordered to Naval Air Station Pensacola, Florida for brief duty as commanding officer of Marine Barracks there and subsequently assumed duty as executive officer of the Marine Corps Rifle range at Wakefield, Massachusetts. He spent next three years with shooting competitions, winning first place in 1911 with Marine Corps rifle team at the Marine Barracks Guantanamo Bay, Cuba and first place at Camp Perry, Ohio, in 1911. He also qualified as Distinguished Marksman in 1911 and received Distinguished Marksman Badge.

He was ordered to Japan in January 1912 and served as assistant naval attache at the American embassy in Tokyo until February 1915. Keyser also became fluent in Japanese language during his service in Japan. Upon his return to the United States, Keyser was ordered as Range officer to the Marine Corps Rifle Range at Winthrop, Maryland and also captained Marine Rifle Team, which won 2nd place at the competition at the Naval Air Station Jacksonville, Florida. He was promoted to the rank of captain in September 1916 and assumed duty as aide to the commandant of the Marine Corps, George Barnett. While in this capacity, Keyser was promoted to the rank of major in May 1917.

Following the entry of the United States into World War I, Keyser requested combat in Europe. His request was granted and Keyser sailed in February 1918 to France where he served as an infantry officer and Marine Corps Intelligence officer. He joined the General Staff of 2nd Army Division under Major General Omar Bundy and served in the Intelligence section until the beginning of June 1918. Keyser subsequently joined 5th Marine Regiment and assumed duty as executive officer of 2nd Battalion under Lieutenant Colonel Frederic M. Wise.

Keyser subsequently took part in the Battle of Belleau Wood in June 1918 and assumed command of 2nd battalion on June 23. He distinguished himself and received his first Silver Star for bravery and led his battalion during the battle of Soissons on July 18, 1918. Keyser distinguished himself while leading the attack in the vicinity of Soissons in order to support of 3rd Brigade advance. His battalion suffered heavy casualties by German artillery, machine guns and snipers hidden in the woods, so Keyser assembled approximately 250 men of his battalion and led them one and half kilometer under enemy fire until they reached the woods of Léchelle. He ordered his men to dig in and placed his command post on the frontline in order to boost morale and fighting spirit. Keyser was slightly wounded on July 20 and ordered back to the staff od 2nd Army Division, now commanded by Marine Major General John A. Lejeune. For his gallantry in action at Soissons, Keyser was decorated together with three Silver Stars, but these decorations were later upgraded to Navy Cross, the United States military's second-highest decoration awarded for valor in combat.

While again on the staff of 2nd Army Division, Keyser served as assistant chief of staff for intelligence (G-2) during the battles of Saint-Mihiel in Meuse Department and Blanc Mont Ridge in Champagne province. He received his second Silver Star for gallantry in action during Blanc Mont Ridge battle.