Riderch I of Alt Clut

Rhydderch Hael (Welsh: Rhydderch the Generous, fl. 580 – c. 614) was a ruler of Alt Clut, a Brittonic kingdom in the Hen Ogledd or "Old North" of Britain. He was one of the most famous kings in the Hen Ogledd, and appears frequently in later medieval works in Welsh and Latin.

According to sources such as the Harleian genealogies and Adomnán's Vita Columbae, Rhydderch's father was Tutagual of Alt Clut, who was probably his predecessor as king. A tyrannical king named Tuduael, Tudwaldus or some variation appears in the 9th-century poem Miracula Nyniae Episcopi and in Ailred of Rievaulx's Vita Sancti Niniani as a contemporary of Saint Ninian; this is possibly a reference to the father of Rhydderch. Genealogies record Rhydderch as a descendant of Dumnagual Hen. Outside of these pedigrees Rhydderch's kinsmen appear only in Welsh texts, chiefly the heroic poetry and the fragments of saga preserved in the Welsh Triads. One such kinsman, Senyllt Hael, is credited in the poem Y Gododdin with him seen presiding over a royal court famed for its liberality. Another, Senyllt's son Nudd Hael, appears with Rhydderch in the triad of the "Three Generous Men of Britain".

In a curious tale preserved in the 12th-century Welsh law code known as the Black Book of Chirk, Rhydderch accompanies other rulers from the North on a military expedition to the Kingdom of Gwynedd in North Wales. According to the story, Elidir Mwynfawr, another prince of the North, had been killed in Arfon in Gwynedd. In response Rhydderch joined Clydno Eiddin, the aforementioned Nudd Hael, and the otherwise unknown Mordaf Hael to seek vengeance on King Rhun Hir ap Maelgwn of Gwynedd. They traveled by sea and ravaged Arfon, but were expelled by Rhun's forces. Rhun attacked Strathclyde and pushed as far as the River Forth.

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