A name or title given to Ambrosius Aurelius in the Vulgate Merlin. It is, without doubt, a simple variant of Pendragon.
Pandragus, Pendragon, Pendragoun, Pendragwn, Uterpandragon
An amalgamation of the Brythonic (a group of Celtic languages comprising Welsh, Cornish and Breton) pen signifying 'head' or 'main' and the Old Welsh dragwn (dragon) meaning 'leader', this title was taken by both Uther and later Arthur, though in the case of the former it has usually been used as a surname. It simply signifies the position of the titleholder as the chief leader.
A title Geoffrey of Monmouth applies to Uther, the father of King Arthur. He is the second son of King Constans of England. When there appears a star with a single ray ending in a fireball shaped like a dragon, Merlin associates the star and the dragon with Uther. Having later become king, Uther has two gold dragons made, one for the cathedral of Winchester, the other to take into battle. Geoffrey tells us that thenceforth he is called Uther Pendragon, which in the British tounge means "dragon's head" and which recognizes both his symbol and his sovereignty as chieftain or king. (In fact, the word apparently means "head dragon" - "foremost leader".) In Arthour and Merlin, Pendragon is the name of Arthur's brother.
In the Prose and Vulgate Merlins, the name Pendragon is given to the character elsewhere called Ambrosius Aurelianus: the son of Constantine and Ivoire, the uncle of Arthur, and the king of Britain between Vortigern and Uther, Pendragonís brother. Pendragon allied with Merlin, defeated Vortigern and Hengist, died fighting the Saxons, Merlin erected Stonehenge as Pandragon's memorial, and Uther adopted his older brother's name in his honor.
Pandragon and his younger brother Uther burned Vortigern in his tower in revenge for Vortigern's barons' murder of their older brother Maines. Pandragon became King, but was killed by the Saxons in battle near Salisbury.
Bearing the same name as Uther Pendragon, this sounds as if it should have been a more important castle than Malory otherwise seems to indicate.
The lord of Pendragon Castle at the time of Sir La Cote Male Taile was Sir Brian de les Isles, "a noble man and a great enemy unto King Arthur". Lancelot vanquished him and freed from his castle thirty of Arthur's knights, including La Cote Male Taile (Brunor the Black), and forty ladies.