John Henry "Doc" Holliday (August 14, 1851 – November 8, 1887) was an American gambler, gunfighter, dentist, and a good friend of Wyatt Earp. He was a Deputy U.S. Marshal during and after the Gunfight at the O.K. Corral.At age 20, Holliday earned a degree in dentistry from the Pennsylvania College of Dental Surgery. He set up practice in Atlanta, Georgia but he was soon diagnosed with tuberculosis, the same disease that had claimed his mother when he was 15.