John Sheldon Doud Eisenhower (August 3, 1922 – December 21, 2013) was a United States Army officer, diplomat, and military historian. He was the second son of President Dwight D. Eisenhower and First Lady Mamie Eisenhower. His military career spanned from before, during, and after his father's presidency, and he left active duty in 1963 and then retired in 1974. From 1969 to 1971, Eisenhower served as United States Ambassador to Belgium during the administration of President Richard Nixon, who was previously his father's vice president and also father-in-law to Eisenhower's son David.