John Milton Hay (October 8, 1838 – July 1, 1905) was an American statesman and official whose career in government stretched over almost half a century. Beginning as a private secretary and an assistant for Abraham Lincoln, he became a diplomat. He served as United States Secretary of State under Presidents William McKinley and Theodore Roosevelt. Hay was also a biographer of Lincoln, and wrote poetry and other literature throughout his life.

Born in Salem, Indiana to an anti-slavery family that moved to Warsaw, Illinois, Hay showed great potential from an early age, and his family sent him to Brown University. After graduation in 1858, Hay read law in his uncle's office in Springfield, Illinois, adjacent to that of Lincoln. Hay worked for Lincoln's successful presidential campaign and became one of his private secretaries in the White House. Throughout the American Civil War, Hay was close to Lincoln and stood by his deathbed after the President was shot. In addition to his other literary works, Hay co-authored, with John George Nicolay, a ten-volume biography of Lincoln that helped shape the assassinated president's historical image.

After Lincoln's death, Hay spent several years at diplomatic posts in Europe, then worked for the New-York Tribune under Horace Greeley and Whitelaw Reid. Hay remained active in politics, and from 1879 to 1881 served as Assistant Secretary of State. Afterward, he returned to the private sector, remaining there until President McKinley, of whom he had been a major backer, made him the Ambassador to the United Kingdom in 1897. Hay became the Secretary of State the following year.

Hay served for nearly seven years as Secretary of State under President McKinley and, after McKinley's assassination, under Theodore Roosevelt. Hay was responsible for negotiating the Open Door Policy, which kept China open to trade with all countries on an equal basis, with international powers. By negotiating the Hay–Pauncefote Treaty with the United Kingdom, the (ultimately unratified) Hay–Herrán Treaty with Colombia, and finally the Hay–Bunau-Varilla Treaty with the newly independent Republic of Panama, Hay also cleared the way for the building of the Panama Canal.