Stanley G. Mortimer III is the son of Stanley G. Mortimer Jr, a member of an illustrious American family. Through Jr.'s father, a Wall Street broker, he was a descendant of John Jay, the first Chief Justice of the United States and a signer of the Declaration of Independence. Jr.'s mother, the former Kathleen Tilford, was the daughter of Henry Morgan Tilford, a founder of the Standard Oil Company of California. During Jr.'s career, he was director of advertising for both Trans World Airlines and Pan American World Airways.
Jr.'s first marriage, in 1940 to Barbara Cushing, ended in divorce in 1946, and she later married Mr. Paley, the longtime leader of CBS. The following year, Mr. Mortimer married Kathleen H. Harriman, daughter of W. Averell Harriman and the granddaughter of E. H. Harriman, the railroad tycoon. W. Averell Harriman served as Secretary of Commerce under President Harry S. Truman and later as the 48th 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.
Stanley III is Jr.'s son from his first marriage.