John Milton Hay (1838-1905) began his public career as a secretary to Abraham Lincoln. His diary and writings during the Civil War are basic historical sources. He is credited by some as being the author of Lincoln's letter to the Widow Bixby, consoling her for the loss of her sons in the war. Hay was present when Lincoln died after being shot at Fords Theatre. Hay and his fellow secretary, John G. Nicolay, wrote a 10-volume biography of Lincoln and prepared an edition of his collected works. Hay was named U.S. ambassador to Great Britain in 1897 when his friend William McKinley became President. Some of the recognition of the longstanding community of interests between that country and the United States came as a result of Hay's stay there. In August 1898, Hay was named Secretary of State and helped negotiate the Treaty of Paris (1898).

His contributions included the adoption of an Open Door Policy in China (announced on January 2, 1900) and the preparations for the Panama Canal. He is also renowned for his comment, written in a letter to President Theodore Roosevelt, describing the Spanish-American War as a "splendid little war."

John Milton Hay is depicted (fictionally) in Gore Vidal's novels Lincoln (novel) and Empire.