Catigern

King of Powys in the 5th century A.D. 
One of the sons of Vortigern, High King of Powys, as part of the Gwertherion dynasty. 
Catigern slew Horsa in Vortimer's battle with the Saxons. 
Also: Cadeyrn Fendigaid, Cedehern, or Cateyrn ap Gwrtheyrn