William Averell Harriman (November 15, 1891  – July 26, 1986) was an American Democratic Party politician, businessman, and diplomat. He was the son of railroad baron E. H. Harriman. He served as Secretary of Commerce under President Harry S. Truman and later as Governor of New York. He was a candidate for the Democratic Presidential Nomination in 1952, and again in 1956 when he was endorsed by President Truman but lost to Adlai Stevenson. Harriman served President Franklin D. Roosevelt as special envoy to Europe and served as the U.S. Ambassador to the Soviet Union and U.S. Ambassador to Britain. He served in various positions in the Kennedy and Johnson administrations. Among his wives were Marie Norton Whitney, who left her husband Cornelius Vanderbilt Whitney to marry him, and Pamela Harriman, former wife of Winston Churchill's son Randolph.

William Averell Harriman was born in New York City, the son of railroad baron Edward Henry Harriman and Mary Williamson Averell, and brother of E. Roland Harriman. Harriman was a close friend of Hall Roosevelt (brother of Eleanor Roosevelt). He attended Groton School in Massachusetts before going on to Yale where he joined the Skull and Bones society. He graduated in 1913.

Using money from his father, in 1922 he established W.A. Harriman & Co, a banking business. In 1927, his brother Roland joined the business and the name was changed to Harriman Brothers & Company. In 1931, they merged with Brown Bros. & Co. to create the highly successful Brown Brothers Harriman & Co.. Notable employees included George Herbert Walker and his son-in-law Prescott Bush.