William McClellan "Mac" Thornberry (born July 15, 1958) is an American politician who served as the U.S. representative for Texas's 13th congressional district from 1995 to 2021. A member of the Republican Party, Thornberry represented the most Republican district in the United States by partisan voting index. The district covers the Texas Panhandle and stretched between the Oklahoma and New Mexico borders. In September 2019, Thornberry announced that he would not run for reelection in 2020, and former Physician to the President Ronny Jackson was elected to succeed him.