Gwenddoleu ap Ceidio

Gwenddoleu ap Ceidio (died c. 573) or Gwenddolau was a Brythonic king who ruled in Arfderydd (now Arthuret). This is in what is now south-west Scotland and north-west England in the area around Hadrian's Wall and Carlisle during the sub-Roman period in Britain. Carwinley near Longtown north of Carlisle is thought to represent Caer Wenddolau or Gwenddolau's Fort.

Genealogies make him a descendant of Coel Hen, who is believed to have ruled much of what is now southern Scotland and the Borders following the Roman withdrawal from the island of Britain, in the area known as the Hen Ogledd. Gwenddoleu was therefore likely to have been either the heir to one of the many successor states of Coel Hen's realm or an usurper who claimed descent from Coel Hen to legitimize his family's claim to the region.

Little is known of his reign, but it ended when, as described in the Annales Cambriae, the sons of Eliffer, Peredur and Gwrgi, the joint kings of Efrog, killed him at the Battle of Arfderydd in 573. It is possible he was succeeded by one of his brothers. This was one of many battles fought between Brythonic kings who led the various fractured successor states that took over the Roman province of Brittania following the Roman withdrawal.

Although Gwenddoleu plays no part in Arthurian legend, his court adviser Myrddin formed part of the basis for the later Arthurian legends concerning the wizard Merlin. In Geoffrey of Monmouth's Vita Merlini, Myrddin (Merlinus) is said to have been driven mad with grief following the death of Gwenddoleu and to have fled into the Caledonian forest. The memory of both Gwenddoleu and Myrddin was preserved in Welsh literature.

...
Wikipedia