Robert L. Thornton, American businessman and politician, Mayor of Dallas (d. 1964)
Robert Lee Thornton, Sr. (often R. L. Thornton; 10 August 1880 – 15 February 1964) was an American banker, civic leader, and four-term Mayor of Dallas, Texas.

Thornton grew up with some schooling, but spent many of his early years working, dividing his time between school and farm labor. Later, he was a store clerk and then a traveling salesman. After two unsuccessful business ventures, Thornton began a banking operation in Dallas in 1916, financed by loans from family. The bank progressed to be a Texas-wide institution, and by 1923 it had a national charter. Thornton served as president (1916 -1947) of the bank he founded, the Mercantile Bank and Trust Co, and board chairman (1947-1964).

Thornton quickly became a prominent businessman and community figure, serving as president of the Dallas Chamber of Commerce (CoC) from 1933 to 1936, and as president of the State Fair of Texas from 1945 to 1960. He was instrumental, along with CoC colleagues, in securing the Texas Centennial Exposition for Dallas. From 1953 to 1961, Thornton served as mayor of Dallas, helping to promote the Forney Dam project on Lake Ray Hubbard, which still supplies the city of Dallas with part of its water needs, and expanding Dallas Love Field, then Dallas's only airport. His vigorous promotion of the city and its development earned him the soubriquet Mr. Dallas in the media. His avuncular and countryfied manner saw him often referred to and addressed as Uncle Bob by locals and associates.

It was during his term as mayor that issues of desegregation became current in Dallas, as in the rest of the South. Both in his capacity as mayor, and in his long-term service as a State Fair official, Thornton used his standing in the communities of Dallas: business, African American, and White, to negotiate contested resolutions to segregation. In the 1920s, Dallas had had one of the highest proportions of Klan membership of any city, just at the time Thornton was rising to prominence. In the 1950s and 60s, his brokered agreements to gradually meet the city’s obligations to integrate, at times disappointed and angered African American campaigners. Despite this, there were no contemporary, or later, suggestions of Klan affiliation until 1994. At that time, Thornton’s family argued that he had never any Klan association, citing the scrutiny Thornton had been under for all his decades of prominence, without any similar claim ever surfacing prior.

Thornton married Mary Metta Stiles in 1904. They settled in Dallas, raising five children there. Thornton died in 1964. Various roads and places in Dallas are named for him. Since the 1990s there have been intermittent calls for these place names to be changed on the basis of Thornton's perceived involvement with the Klan. Although no firm evidence of any such involvement appears to exist, the claim of his membership is repeated from time-to-time in various media outlets.