Pendragon or Pen Draig, meaning in Welsh "head (Pen) dragon (Draig) " or "chief dragon" (a figurative title referring to status as a leader and shortened from Pen y Ddraig (pronounced Thraig as in 'then, there, thus')), is the name of several traditional Kings of the Britons: Ambrosius Aurelianus, son of Constantine II of Britain (called "Pendragon" in the Vulgate Cycle); Uther, brother of Aurelius and father of King Arthur (called "Uther Pendragon" because he was inspired by a dragon-shaped comet); King Arthur, son of Uther Pendragon; and Maelgwn of Gwynedd, described by Gildas as the "dragon of the island."
In the prose version of Robert de Boron's Merlin, the name of Uther's elder brother Ambrosius is given as "Pendragon", while Uter (Uther) changes his name after his brother's death to "Uterpendragon".
The use of "Pendragon" to refer to Arthur, rather than to Uther or his brother, is of much more recent vintage. In literature, one of its earliest uses to refer to Arthur is in Alfred Tennyson's poem Lancelot and Elaine, where, however, it appears as Arthur's title rather than his surname, following contemporary speculation that "pendragon" had been a term for an ancient Welsh war-chief.
Mark Twain in A Connecticut Yankee in King Arthur's Court makes various satirical and scathing remarks about "The Pendragon Dynasty" which are in fact aimed at ridiculing much later British dynasties.