John Henry "Doc" Holliday (August 14, 1851 – November 8, 1887) was an American gambler, gunfighter and dentist of the American Old West, who is usually remembered for his friendship with Wyatt Earp and his involvement in the Gunfight at the O.K. Corral.
As a young man, Holliday earned a D.D.S. degree in dentistry and set up a practice in Atlanta, Georgia. However, in 1873 he was diagnosed with tuberculosis, the same disease that had claimed his mother when he was 15. He moved to the American southwest in hopes that the climate would prolong his life. Taking up gambling as a profession, he acquired a reputation as a deadly gunman.

During his travels, he met and became good friends with Wyatt Earp and Earp's brothers. In 1880, he moved to Tombstone, Arizona, and participated alongside the Earps in the famous gunfight. This did not settle matters between the two sides, and Holliday was embroiled in ensuing shootouts and killings. He successfully fought being extradited for murder, and died in bed at a Colorado hotel/sanatorium at the age of 36.

The legend and mystique of his life is so great that he has been mentioned in countless books, and portrayed by various actors in numerous movies and television series. For the 100-plus years since his death, debate has continued about the exact crimes he may have committed during his life.