He was born Clement Alexander Finley Flagler in Augusta, Georgia, the son of Brigadier General Daniel Webster Flagler, for whom Fort Flagler, Washington was named. The younger Flagler was named for his maternal grandfather, Army Surgeon General Clement Alexander Finley. Known as Clement Flagler, Clement A.F. Flagler, and C.A.F Flagler, he grew up in Iowa while his father commanded the Rock Island Arsenal. In 1885 he received a bachelor of science degree from Griswold College. He then accepted appointment to the United States Military Academy after being recommended by Congressman Jerry Murphy. He graduated in 1889, and Flagler's high class ranking enabled him to obtain a sought after position in the Army's Engineer branch. While at West Point Flagler was nicknamed "Sioux" as a testament to his dark eyes, hair, and complexion, his having been raised in Iowa, and his self-professed Native American heritage, and his classmates used it with him for the rest of his life.
Start of military career
Assigned as an Engineer officer, Flagler served as instructor in civil and military engineering at West Point, and as engineer officer at Chickamauga, Georgia.
Spanish–American War
During the Spanish–American War Flagler was temporarily promoted to Major and assigned as engineer officer on the staff of the U.S. Army commander in Puerto Rico.
During Mexican border skirmishes of 1914–1916, Flagler served on General Funston's staff in the Vera Cruz Expedition.
World War I
During World War I, Flagler successively commanded the 7th Engineer Regiment, 5th Infantry Division Artillery, III Corps Artillery, and the 42nd Infantry Division, attaining the temporary rank of Major General.
Post World War I
After World War I Flagler served as commandant of the Army's Engineer School at Camp Humphreys, Virginia and then chief engineer of the department based in Honolulu, Hawaii. In 1921 Flagler was assigned to Baltimore as chief engineer of the Eastern Division, the post in which he was serving when he died.
Military awards
General Flagler was a recipient of the Legion of Honor and the Croix de Guerre for his World War I service.
In 1897, Flagler married Mrs. Caroline DeWitt Quinan in Salt Lake City. Caroline DeWitt had children with her first husband, William R. Quinan, from whom she was divorced in 1896, but none with Flagler.
Legacy
Flagler Road, which runs between 18th and 21st Streets at Fort Belvoir, and includes the post headquarters, is named for him. Fort Belvoir was previously the location of the Army Engineer Center and School, and several streets and buildings there are named for prominent Engineer officers.