Eudaf Hen (Eudaf "the Old") 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 Wledig and Geoffrey of Monmouth's Latin chronicle Historia Regum Britanniae. He also figures into Welsh genealogies. Geoffrey of Monmouth calls him Octavius, 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. Etymology 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 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 (Eudaf Hen), 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. Eventually, Caradocus, Duke of Cornwall, suggests that Octavius marry his only daughter Helen to the new Roman Emperor, Maximianus (Magnus Maximus), thereby uniting the British and Roman crowns. Octavius agrees, and Caradocus' son Mauricius is sent to Rome with the proposal. However Octavius' nephew Conan Meriadoc (elsewhere his son) opposes the union, and nearly attacks the arriving Maximianus. Finally Caradocus restores the peace, and Octavius abdicates the throne in favor of Maximianus. The Breton Life of Saint Gurthiern Utilizing an