Eudaf Hen

Eudaf Hen (Eudaf "the Old") or Octavius is a figure of Welsh tradition. He is remembered as a King of the Britons and the father of Elen Luyddog and Conan Meriadoc in sources such as the Welsh prose tale The Dream of Macsen and Geoffrey of Monmouth's Latin chronicle Historia Regum Britanniae. He also figures into Welsh genealogies. The name Octavius in Geoffrey of Monmouth Historia is a corruption and faux-Latinization of Old Welsh/Breton Outham (later spelled Eudaf). According to the medieval Welsh genealogy from Mostyn MS. 117, Eudaf was a direct ancestor of King Arthur.

Modern Welsh Eudaf (Middle Welsh Eudav, early Old Welsh Out(h)am) comes from Brittonic *Aui-tamos meaning "Very Strong in Will".

Geoffrey of Monmouth, in his Historia Regum Britanniae, renders the name in pseudo-Latin form as Octavius and introduces him as a half-brother to Constantine I, who has become King of the Britons following the death of his father Constantius. Eventually Constantine is made Roman Emperor, requiring him to leave Britain in the hands of a proconsul. Octavius, then duke of the Gewissei tribe, rebels against Roman rule, killing the proconsul and proclaiming himself king.

Constantine responds by sending three legions to Britain under the command of his great-uncle Trahern, the brother of the late King Coel. Trahern lands at "Kaerperis" and captures it, forcing Octavius to conscript all the island into the army to combat the Roman legions. Octavius engages Trahern in a field outside Winchester and is victorious. Trahern flees to Alba (Scotland) and pillages the land, and Octavius comes after him. They meet at Westmorland, and Octavius was defeated and forced out of Britain. Trahern takes the crown himself, while Octavius seeks aid from King Gunbert of Norway. In Britain, supporters of Octavius ambush Trahern and kill him near London, allowing Octavius to return to Britain. Once arrived, he scatters the Roman forces and retakes the throne of Britain, gaining an incredible amount of wealth and prestige.

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