Mellon, Andrew William (1855–1937), a United States financier and statesman. He was secretary of the treasury for 11 years, from 1921 to 1932 under Presidents Harding, Coolidge, and Hoover. Under Mellon the national debt of the United States was reduced by some $8,000,000,000. His program for tax reform was largely adopted by Congress, resulting in a substantial reduction in taxes. Mellon served as ambassador to Great Britain, 1932–33.

Mellon was born in Pittsburgh, Pennsylvania. He attended the Western University of Pennsylvania (now the University of Pittsburgh) before entering the lumber and building business. In 1874 he joined his father's banking firm of T. Mellon & Sons, the ownership of which his father gave him in 1882. (In 1902 it was chartered as the Mellon National Bank.)

In 1889 Mellon became president of the Union Trust Company, formed by him and Henry Clay Frick. Mellon helped found the Aluminum Corporation of America and acquired interests in the coal, coke, oil, steel, and construction industries. His investments brought him vast wealth and influence. He became a large contributor to the Republican party.

Mellon and his brother Richard founded the Mellon Institute of Industrial Research in 1913. (The institute later merged with Carnegie Institute of Technology to become Carnegie-Mellon University.) In 1937 Mellon gave the United States his magnificent art collection and funds for a building in which to house it. The result is the National Gallery of Art in Washington, D.C.