Robert Lee Thornton, banker, civic leader, and mayor of Dallas, was born near Hico, Texas, on August 10, 1880, to William Travis and Polly Ann (Weatherby) Thornton. Having lost their farm because of a title flaw, the family moved to Village Creek, near Ennis, where, as a seven-year-old, Thornton learned to pick a bale of cotton a day. In Bristol he sporadically attended public school, ultimately completed eight grades, and worked as a store clerk. With money borrowed from his boss he took a business course at the Metropolitan Business College in Dallas. In 1904 he became a traveling candy salesman with a St. Louis company, for which he worked the Indian Territory out of his Dallas home base. His attempts at a book and stationery company, Thornton and Bracey, and a mortgage company failed, but in 1916, with $12,000 in notes from one of his wife's brothers and $6,000 cash from another, he became president of Stiles, Thornton, and Lund, a private banking house. In 1917 the company organized the Dallas County State Bank, which during the Great Depression became a national bank, the Mercantile. Thornton served as president from 1916 to 1947, when he became chairman of the board. He was the first Dallas banker to make automobile loans. The state's bankers recognized him by making him president of the Texas Bankers Association in 1924–25. He was also vice president of Tex-O-Kan Flour Mills Company and United Fidelity Life Insurance Company, and a director of the Weatherford, Mineral Wells and Northwestern Railway, Lone Star Steel, Dallas Power and Light, Southwestern Life Insurance, Burrus Mills, and the Dallas Hotel Company. Thornton also owned and operated a ranch in Argyle, Texas, where he raised registered Aberdeen-Angus cattle.
Although he was acknowledged as a successful businessman, it was Thornton's civic involvement that caused journalists to begin calling him "Mr. Dallas." Through his efforts as president of the Dallas Chamber of Commerce (1933–36), the city hosted the Texas Centennial Exposition (1936), for which Thornton also served as a director and member of the executive committee. He helped organize the Dallas Citizens Council, an organization of presidents or owners of Dallas businesses called the "blue ribbon group that has ever since influenced the direction of the city." Thornton was a director of the Greater Texas and Pan-American Exposition in 1937 and president of the State Fair of Texas from 1945 to 1960, when he resigned to become chairman of the board. He is credited with building the fair into the nation's biggest. During his mayoralty (1953–61) Thornton's motto, "Keep the dirt flying," was exemplified in his promotion of the Forney Dam project, which provided for the city's future water needs, and the completion of the Love Field expansion and a new city hall, library, and auditorium. Thornton was a member of the Greater Dallas Council of Churches Executive Committee and a director of the Southwestern Medical Foundation (see UNIVERSITY OF TEXAS SOUTHWESTERN MEDICAL CENTER, DALLAS), the Texas Research Foundation, the Dallas Clearing House Association, the Trinity Improvement Association, the Dallas Civic Opera, the Dallas Symphony Orchestra, and the Dallas Community Chest. Among his numerous awards and citations are the Linz Award for outstanding civic contributions (1947), the Sales Executive Club's Number 1 Salesman of Dallas award (1948), the Greater Dallas Planning Council's Distinguished Citizen Award (1955), the Press Club's Headliner of the Year award (1955), the Man of Vision Award from the Dallas Chapter of the American Institute of Architects (1959), and an honorary doctor of humanities degree from the University of Dallas (1963). Thornton Freeway in Dallas is named in his honor. Thornton married Mary Metta Stiles on June 1, 1905; they had three children. He was a Democrat, a Mason, and a Methodist. Thornton was in failing health for several years before he died at his home in Dallas on February 15, 1964.