The dentist and gunfighter appears in Spectre of the Gun as one of the Earp faction in the Melkotians' recreation of Tombstone, and is visited in his surgery by Doctor McCoy.
John Henry Holliday, the dentist turned gambler and gunman who stood with the Earps at the O.K. Corral, appears in the Original Series episode Spectre of the Gun, played by Sam Gilman.
In the Melkotian illusion of Tombstone the Enterprise landing party are taken for the Clantons, and McCoy is addressed as one of the McLaury brothers. Needing supplies for a tranquilliser that Spock and Scott hope to use against the Earps, McCoy calls at Holliday's surgery and borrows what he needs, the two doctors managing a brief professional courtesy despite the feud.
Holliday carries a shotgun to the final confrontation and fires with the Earps, but the shots have no effect on men who no longer believe in them.