TRAHAERN ap CARADOG (d. 1081), king of Gwynedd. He is said to have been the son of one Caradog ap Gwyn ap Collwyn and a cousin of Bleddyn ap Cynfyn. By natural right ruler of Arwystli, his career between 1075 and 1081 is one of the foremost illustrations in Welsh history of how a bold and ambitious personality among the minor lords of Wales could usurp regal powers over an extensive area at moments when the fortunes of the major dynasties were at a low ebb. On Bleddyn's death in 1075, he seized authority in Gwynedd. Challenged by Fruffudd ap Cyana, the representative of the old Venodotian house, he was defeated at Dyffryn Glyngin in Meirionydd, but later in the year he retrieved himself at Bron yr Erw and drove Gruffudd into second exile in Ireland. In 1078 he invaded South Wales and killed its king (Rhys ab Owain) at Goodwick. The general threat to old established interests eventually brough Gruffudd and Rhys ap Tewdwr into alliance, and together they imposed a crushing defeat on their opponent at the well-known battle of Mynydd Carn. fought in 1081, and in which Trahaearn met his end. He left four sons-Meurig, Griffi, Llywarch, and Owain. His descendants ruled in Arwystli until it was absorbed into Powys by Gwenwynwyn. A grand-daughter, Gwladus, m. Owain Gwynedd; her son was Iorwerth Drwyndwn, father of Llywelyn the Great.
Sources: J. E. A History of Wales, 1911 (last edn. 1930); Dictionary of National Biography; _Life of Gruffudd ap Cynan. T.J.P. [Ref: The Dictionary of Welsh Biography Down to 1940, editors, Sir John Edward Lloyd & R. T. Jenkins, (1959), p. 976]