Thornton grew up with some schooling, but spent many of his early years working - first as a cotton picker, then as a store clerk and later as a traveling salesman. In 1916, Thornton founded Stiles, Thornton and Lund, a banking company, called the Mercantile National Bank, serving as its president through 1947. In 1942, Thornton saw the completion of the bank's headquarters, the Mercantile Bank Building. By 1917, the company organized the Dallas County State Bank  which became one of the national banks during the Great Depression.
Thornton quickly became a prominent businessman, being named to high positions with other local business in various industries, including insurance, railroads, steel, the local utility company, and hotels. Thornton also raised cattle at a ranch he owned in Argyle, Texas.
Thornton was also a prominent figure in the community, serving as president of the Dallas Chamber of Commerce from 1933 to 1936, President of the Rotary Club of Dallas 1915-1916 and serving as president of the State Fair of Texas from 1945 to 1960.
From 1953 to 1961, Thornton served as mayor of Dallas, helping to promote the Forney Dam project on Lake Ray Hubbard, which still helps to supply the city of Dallas with its water needs and expanding Love Field, Dallas's only airport at the time.
After Thornton died in 1964, he was still well-remembered. Interstate 30 east of downtown (E R. L. Thornton Freeway) and Interstate 35E south of downtown (S R. L. Thornton Freeway) are named for him, as is the headquarters building of the Dallas County Community College District in downtown Dallas.
Thornton's grandson, Robert L. Thornton III, has also followed in his grandfather's footsteps as a city businessman and philanthropist.References
- Texas Labor History
- Peep-hole power, page 1 - News - Dallas Observer - Dallas Observer
- White Metropolis By Michael Phillips
- Wikipedia, http://en.wikipedia.org/wiki/Robert_L._Thornton