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.