Rhodri the Great (in Welsh, Rhodri Mawr; occasionally in English, Roderick the Great) (c. 820–878) was the first ruler of Wales to be called 'Great', and the first to rule most of present-day Wales. He was called King of the Britons by the Annals of Ulster.
The son of Merfyn Frych ap Gwriad king of Gwynedd and Nest ferch Cadell of the royal line of Powys, he inherited the kingdom of Gwynedd on his father's death in 844. When his uncle Cyngen ap Cadell ruler of Powys died on a pilgrimage to Rome in 855 Rhodri inherited Powys. In 872 Gwgon, ruler of Seisyllwg in southern Wales, was accidentally drowned, and Rhodri added his kingdom to his domains by virtue of his marriage to Angharad, Gwgon's sister. This made him the ruler of the larger part of Wales.
Rhodri faced pressure both from the English and increasingly from the Danes, who were recorded as ravaging Anglesey in 854. In 856 Rhodri won a notable victory over the Danes, killing their leader Gorm (sometimes given as Horm). Two poems by Sedulius Scotus written at the court of Charles the Bald, king of the Western Franks, celebrate the victory of "Roricus" over the Norsemen.
In 877 Rhodri fought another battle against the Norse invaders on Anglesey, this time being forced to flee to Ireland. On his return the following year, he and his son Gwriad were said to have been killed by the English under Alfred the Great, though the precise manner of his death is unknown. When his son, Anarawd ap Rhodri won a victory over the Mercians a few years later, it was hailed in the annals as "God's vengeance for Rhodri".
His son Cadell ap Rhodri conquered Dyfed, which was later joined with Seisyllwg by Rhodri's grandson Hywel Dda to become Deheubarth. Like his grandfather, Hywel would come to rule to bulk of Wales.
(From Wikipedia, the free encyclopedia)
RODERIC MAWR, or the Great, who succeeded as King of Wales 843 and was slain at Anglesea in a battle against the English 876; married Anghared, daughter and heiress of Merich Dyfnwal ap Arthen ap Silsylht, King of Cardigan, and sister and heir of Gwygan ap Merick, Lord of Cardigan.
(Fenwick Allied Ancestry, page 181)