Vortigern

5th century warlord and High King of Powys. He ruled from Gwrtheyrnion, as the ruler of the Rhwng Gwy a Hafren.
Vortigern invited the Saxons Hengist and Horsa to aid him in fighting the Picts, as he also pitted them against the sons of Constantine III for his own treasury and land in the Welsh Marches. 
He is the founder of the Gwertherion Dynasty, a line of kings who were his descendants. His four sons were Vortimer, Catigern, Pascent, and Faustus. Vortigern also has several daughters, including one named Vortella, and Vortis. 
Also: Gwrtheyrn, Wyrtgeorn, or Vortigernus