Who was the first US President to donate his entire salary to charity?

Herbert Clark Hoover ( born August 10, 1874 – died October 20, 1964) was the 31st President of the United States (1929–33). He was a professional mining engineer and was raised as a Quaker. A Republican, Hoover served as head of the U.S. Food Administration during World War I, and became internationally known for humanitarian relief efforts in war-time Belgium. As the United States Secretary of Commerce in the 1920s under Presidents Warren G. Harding and Calvin Coolidge, he promoted partnerships between government and business under the rubric "economic modernization".

Before becoming US President, Hoover made a small fortune in mining, He was the first of two US Presidents (John F. Kennedy being the second) to donate all of his presidential salary to charity. When he first got into politics, he decided to never accept money for performing any public service, so that no one would ever accuse him of corruption.