Cadell Ddyrnllwg

King of Powys in the 5th century A.D. 
One of the sons of Catigern, as part of the Gwertherion dynasty, and a brother of Rhyddfedd Frych.
Cadell was driven out of his father Catigern's kingdom by Irish pirates during the chaos of the Saxon insurrection in Southern Britain. He hid himself amongst the peasants of Powys, and became a servant of the Irish chieftain Benlli, hoping, one day, to find an opportunity to retrieve his inheritance. His chance arose when Roman clergyman, St. Germanus of Auxerre, visited Britain, probably for the second time in A.D. 447, to combat Pelagian views. Travelling into the Midlands, St. Germanus heard of the pagan Irish stronghold and, with his many followers, laid siege to the Powysian capital, located at a Clwydian hillfort at the time; Foel Fenlli, or the Hill of Benlli. Cadell showed them what modest hospitality he could in his rural hovel outside the city walls. Germanus eventually had a dreadful premonition and advised Cadell to remove all his friends from within the city walls. That night, the Royal palace was struck by lightning. The resulting fire spread quickly and all within the city were burnt alive. The young Cadell was thus restored to his throne.
Cadell married Gwelfyl, one of the many daughters of King Brychan Brycheiniog. They had a number of children, including Tegid, the father of Gwynllyw, and possibly Gwynfyr Frych, Ystradwel and Ddewer.
Cadell Ddyrnllwg is Welsh for "Cadell of the Gleaming Hilt"