Rhodri Mawr who died in the year 877
(Mawr in Welch is "The great")
was a one time king of Wales and ancestor in the Owain / Owen clan of Gwynned read below for information about the descendants of Rhodri.
I have some information on the web site about the Bowens Welch origins
http://freepages.family.rootsweb.com/~bowen/origins.html
and this from David Fortins Welch history:
.....During this period, one of the great figures of Welsh history appears onthe scene, Rhodri Mawr. We know little of him, other than the references in the annals, some legends, geneologies, and references to his sons in Asser. Once again, I will be relying upon the work of JE Lloyd and John Davies. Upon the death of Hywel ap Rhodri Molwynog (the Hywel in the above annal) in 825, the direct male line of Gwynedd seems to have ended. Upon his death a certain Merfyn Frych (the Freckled) came to the royal seat of Aberffraw. Merfyn was supposedly descended from Llywarch Hen (of poetic fame) and according to bardic tradition was "from the land of Manaw", which either meant he was from the Isle of Man or was from the area which used to be the kingdom of Gododdin (or was descended from the royal house of Gododdin). At any rate, he was able to secure his hold on Gwynedd and in 844, passed the kingdom to his son, Rhodri.
Rhodri Mawr was able to do something which no other ruler in Wales had been able to do: forge a kingship which extended over much of Wales. he was able to accomplish this through some timely deaths of relatives and marriage alliances. In the end, when he died in 877, he was ruler over Gwynedd, Powys (through marriage allaince), and Seisyllwg (the southern cantrefi and Ceredigion, through the death of his brother-in-law). However, Rhodri earned his title of Mawr (the Great) through his victory over the Vikings in 856, during which he killed the Danish leader Gorm. This victory was celebrated throughout Western Europe, with a legthy poem by Sedulus Scotus, an Irish monk living in Carolingian Frankia.
Rhodri died in 877, while fighting the English. His kingdom was divided amongst his six sons, in accordance with Welsh tradition.
more can be found here :
http://freepages.history.rootsweb.com/~bowen/welchist2.html
Also this ancient material from Geraldus Cambrensis work :
The description of Wales :
Chapter II
Of the ancient division of Wales into three parts
Wales was in ancient times divided into three parts nearly equal, consideration having been paid, in this division, more to the value than to the just quantity or proportion of territory. They were Venedotia, now called North Wales; Demetia, or South Wales, which in British is called Deheubarth, that is, the southern part; and Powys, the middle or eastern district. Roderic the Great, or Rhodri Mawr, who was king over all Wales, was the cause of this division. He had three sons, Mervin, Anarawt, and Cadell, amongst whom he partitioned the whole principality. North Wales fell to the lot of Mervin; Powys to Anarawt; and Cadell received the portion of South Wales, together with the general good wishes of his brothers and the people; for although this district greatly exceeded the others in quantity, it was the least desirable from the number of noble chiefs, or Uchelwyr, men of a superior rank, who inhabited it, and were often rebellious to their lords, and impatient of control. But Cadell, on the death of his brothers, obtained the entire dominion of Wales, as did his successors till the time of Tewdwr, whose descendants, Rhys, son of Tewdwr, Gruflydd, son of Rhys, and Rhys, son of Gruffydd, the ruling prince in our time, enjoyed only (like the father) the sovereignty over South Wales.
Chapter III
Genealogy of the Princes of Wales
The following is the generation of princes of South Wales: Rhys, son of Gruffydd; Gruffydd, son of Rhys; Rhys, son of Tewdwr; Tewdwr, son of Eineon; Eineon, son of Owen; Owen, son of Howel Dda, or Howel the Good; Howel, son of Cadell, son of Roderic the Great. Thus the princes of South Wales derived their origin from Cadell, son of Roderic the Great. The princes of North Wales descended from Mervin in this manner: Llewelyn, son of Iorwerth; Iorwerth, son of Owen; Owen, son of Gruffydd; Gruffydd, son of Conan; Conan, son of Iago; Iago, son of Edoual; Edoual, son of Meyric; Meyric, son of Anarawt (Anandhrec); Anarawt, son of Mervin, son of Roderic the Great. Anarawt leaving no issue, the princes of Powys have their own particular descent.
More can be found here.
http://freepages.history.rootsweb.com/~bowen/geraldusbook1.html