Stanley G. Mortimer III is the son of Stanley G. Mortimer Jr, director of advertising for both Trans World Airlines and Pan American World Airways. 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. Jr.'s first marriage, in 1940 to Barbara Cushing, ended in divorce in 1946, and she later married William 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. Stanley III is Jr.'s son from his first marriage.