King of the Britions

noun

1a traditional story sometimes popularly regarded as historical but not authenticated: the legend of King Arthur [mass noun]: according to legend he banished all the snakes from Ireland.

  
Arthur, King of the Britons

A biography by me

Arthur, it seems, is claimed as the King of nearly every Celtic Kingdom known. The 6th century certainly saw many men named Arthur born into the Celtic Royal families of Britain but, despite attempts to identify the great man himself amongst them, there can be little doubt that most of these people were only named in his honour. Princes with other names are also sometimes identified with "Arthwyr" which is thought by some to be a title similar to "Vortigern".
Breton King
Geoffrey of Monmouth recorded Arthur as a High-King of Britain. He was the son of his predecessor, Uther Pendragon and nephew of King Ambrosius. As a descendant of High-King Eudaf Hen's nephew, Conan Meriadoc, Arthur's grandfather, had crossed the Channel from Brittany and established the dynasty at the beginning of the 5th century. The Breton King Aldrien had been asked to rescue Britain from the turmoil in which it found itself after the Roman administration had departed. He sent his brother, Constantine, to help. Constantine appears to have been the historical self-proclaimed British Emperor who took the last Roman troops from Britain in a vain attempt to assert his claims on the Continent in 407. Chronologically speaking, it is just possible he was King Arthur's grandfather. Arthur's Breton Ancestry was recorded by Gallet.

Riothamus the King
Geoffrey Ashe argues that King Arthur was an historical King in Brittany known to history as Riothamus, a title meaning "Greatest-King". His army is recorded as having crossed the channel to fight the Visigoths in the Loire Valley in 468. Betrayed by the Prefect of Gaul, he later disappeared from history. Ashe does not discuss Riothamus' ancestry. He, in fact, appears quite prominently in the pedigree of the Kings of DomnonŽe, dispite attempts to equate him with a Prince of Cornouaille named Iaun Reith. Riothamus was probably exiled to Britain during one of the many civil wars that plagued Brittany. He later returned in triumph to reclaim his inheritance, but was later killed in an attempt to expel Germanic invaders. The main trouble with this Arthurian identification is that it pushes King Arthur back fifty years from his traditional period at the beginning of the sixth century (See Ashe 1985).