Thomas Claiborne (or Clayborne) Frost, lawyer, merchant, and founder of Frost National Bank, was born in Belle Font, Jackson County, Alabama, on December 31, 1833, the son of Thomas C. and Crissy (Price) Frost. He graduated from Irving College in Tennessee in 1853 and was awarded a professorship in Latin for one year. In 1854 he arrived in Texas as an assistant professor of Latin at Austin College in Huntsville. He studied law in Sam Houston's office and at the office of Henderson King Yoakum and was admitted to the bar around 1856. Apparently he moved to Comanche County, where he practiced law and worked as a surveyor. During this time he also served with the Texas Rangers. On November 30, 1858, he married Mrs. Betty Eastland Roberts at Belton, Texas. They had several children, but only one daughter lived to adulthood. In early 1861 Frost was a member of the Secession Convention in Austin and signed the Articles of Secession. During the Civil War he served as a lieutenant colonel of the First Mounted Rifles. At the end of the war, having refused to take the oath of allegiance to the Union, Frost could no longer practice law. He established a freight business between San Antonio and the port of Indianola. Soon after, his brother John Frost asked him to join him in the mercantile and auction business. Together with a third partner, they successfully operated the firm Fitch, Frost and Brother in San Antonio. In 1868 Frost opened a general store on Main Plaza in San Antonio. Upon his brother's death, Thomas Frost added a new dimension to his enterprise: the wool commission business. He collected and stored local wool producer's goods until market conditions were favorable, making loans to them on the wool stock he was holding. This enterprise furnished the seeds for his banking endeavors. After the death of his first wife, Frost married Josephine Houston on December 31, 1878. They had four children.
On November 30, 1892, Frost purchased Messrs. Thornton, Wright and Company, a banking business. Eventually he formed a partnership with J. T. Woodhull and J. P. Barclay. The banking firm later dissolved, but on February 20, 1899, Frost National Bank received its national charter. Thomas C. Frost served as president until his death in San Antonio on November 21, 1903. After Frost's death, his son, Thomas C., took over as president until 1926, after which another son, Joseph H., became president. Frost Bank continued to grow, merging with Lockwood National Bank in 1928. The bank remained financially sound through the Great Depression and continued to expand operations during the second half of the twentieth century. By the 1990s Frost Bank was a leading financial institution in South Texas, with eighteen locations in San Antonio, Boerne, Austin, and Corpus Christi; it was part of Cullen/Frost Bankers, Incorporated, a Texas holding company with member banks in Dallas, Houston, and Galveston, as well as in markets served by Frost.