John Henry Holliday, better known as Doc Holliday, was an American dentist, gambler, and gunfighter who was a close friend and associate of lawman Wyatt Earp. Holliday is best known for his role in the events surrounding and his participation in the gunfight at the O.K. Corral in Tombstone, Arizona. He developed a reputation as having killed more than a dozen men in various altercations, but modern researchers have concluded that, contrary to popular myth-making, Holliday killed only one to three men. Holliday's colorful life and character have been depicted in many books and portrayed by well-known actors in numerous movies and television series.

At age 20, Holliday earned a degree in dentistry from the Pennsylvania College of Dental Surgery. He set up practice in Griffin, Georgia, but he was soon diagnosed with tuberculosis, the same disease that had claimed his mother when he was 15 and his sister before his birth, having acquired it while tending to his mother's needs. Hoping the climate in the American Southwest would ease his symptoms, he moved to that region and became a gambler, a reputable profession in Arizona in that day. Over the next few years, he reportedly had several confrontations. He saved Wyatt Earp's life during a saloon confrontation in Texas, and they became friends. In 1879, he joined Earp in Las Vegas, New Mexico, and then rode with him to Prescott, Arizona, and then Tombstone. While in Tombstone, local members of the outlaw Cochise County Cowboys repeatedly threatened him and spread rumors that he had robbed a stagecoach. On October 26, 1881, Holliday was deputized by Tombstone city marshal Virgil Earp. The lawmen attempted to disarm five members of the Cowboys near the O.K. Corral on the west side of town, which resulted in the famous shootout.

Following the Tombstone shootout, Virgil Earp was maimed by hidden assailants while Morgan Earp was killed. Unable to obtain justice in the courts, Wyatt Earp took matters into his own hands. As the recently appointed deputy U.S. marshal, Earp formally deputized Holliday, among others. As a federal posse, they pursued the outlaw Cowboys they believed were responsible. They found Frank Stilwell lying in wait as Virgil boarded a train for California, and Wyatt Earp killed him. The local sheriff issued a warrant for the arrest of five members of the federal posse, including Holliday. The federal posse killed three other Cowboys during late March and early April 1882, before they rode to the New Mexico Territory. Wyatt Earp learned of an extradition request for Holliday and arranged for Colorado Governor Frederick Walker Pitkin to deny Holliday's extradition. Holliday spent the few remaining years of his life in Colorado. He died of tuberculosis in his bed at the Hotel Glenwood at age 36.