Maelgwn Hir ap Cadwallon

Maelgwn Gwynedd (Latin: Maglocunus; died c. 547) was king of Gwynedd during the early 6th century. Surviving records suggest he held a pre-eminent position among the Brythonic kings in Wales and their allies in the "Old North" along the Scottish coast. Maelgwn was a generous supporter of Christianity, funding the foundation of churches throughout Wales and even far beyond the bounds of his own kingdom. Nonetheless, his principal legacy today is the scathing account of his behavior recorded in De excidio et conquestu Britanniae by Gildas, who considered Maelgwn a usurper and reprobate. The son of Cadwallon Lawhir and great grandson of Cunedda, Maelgwn was buried on Ynys Seiriol (now known as Puffin Island in English), off the eastern tip of Anglesey, having died of the "yellow plague", quite probably the arrival of Justinian's Plague to Britain.

Maelgwn (IPA: /mɑːɨlgʊn/) in Welsh literally means "Princely Hound" and is composed of the elements mael "prince" (*maglo- in earlier, Common Brittonic) and cwn, the old oblique case form of ci "hound, dog" (from Common Brittonic nominative singular *cū, oblique *cun-). As "hound" was sometimes used as a kenning for a warrior in early Welsh poetry, the name may also be translated as "Princely Warrior".

After the collapse of Roman authority in Britain, north Wales was invaded and colonized by Gaelic tribes from Ireland. The kingdom of Gwynedd began with the reconquest of the coast by northern Britons under the command of Maelgwn's great-grandfather Cunedda Wledig. Generations later, Maelgwn's father Cadwallon Long-Hand completed the process by destroying the last Irish settlements on Anglesey. Maelgwn was the first king to enjoy the fruits of his family's conquest and he is considered the founder of the medieval kingdom's royal family. He is thus most commonly referenced by appending the name of the kingdom to his own: Maelgwn Gwynedd.

...
Wikipedia