George Henry Thomas (July 31, 1816 – March 28, 1870) was a career United States Army officer and a Union General during the American Civil War, one of the principal commanders in the Western Theater. Thomas served in the Mexican-American War and later chose to remain with the United States Army for the Civil War, despite his heritage as a Virginian. He won one of the first Union victories in the war, at Mill Springs in Kentucky, and served in important subordinate commands at Perryville and Stones River. His stout defense at the Battle of Chickamauga in 1863 saved the Union Army from being completely routed, earning him his most famous nickname, the "Rock of Chickamauga." He followed soon after with a dramatic breakthrough on Missionary Ridge in the Battle of Chattanooga. In the Franklin-N