King Arthur was a legendary figure in ancient stories on Earth. Arthur was associated with Camelot and the Knights of the Round Table, which included his knights Galahad, Gawain and Lancelot. Arthur also had an ally in the wizard Merlin.
In 1889, Samuel Clemens wrote A Connecticut Yankee in King Arthur's Court, a time travel story of a person from the 19th century meeting King Arthur. In 1893, Data overheard Clemens remark to a reporter that the time-traveling ideas in the novel weren’t so farfetched. The reporter thought Clemens was describing an upcoming sequel. (TNG episode: "Time's Arrow")
In 1958, the novel The Once and Future King was published. Based on the legends of King Arthur, Merlin was portrayed as living backwards in time, growing younger as he aged. (TOS novel: Strangers from the Sky)
In 2270, Garth of Izar thanked James T. Kirk for believing in him. To Kirk, Garth was a hero from his Starfleet Academy days, and Kirk felt as though King Arthur had just knighted him. (TOS novel: Garth of Izar)
- DS9 episode: "The Way of the Warrior"
- DS9 episode: "The Muse"
- TNG episode: "Time's Arrow"
- TOS novel: Strangers from the Sky
- TOS novel: Shadow Lord
- TOS novel: Best Destiny
- TOS novel: Shell Game
- TOS novel: Garth of Izar
- TOS novel: The Joy Machine
- TOS novel: The New Voyages (introduction)
- TNG novel: Here There Be Dragons
- DS9 novel: Cardassian Imps
- VOY novel: Ghost Dance
- NF novel: Restoration
- NF novel: Fire on High