Son of Branwen and Matholwch (king of Ireland); the foundational Welsh-Irish-half-blood child whose existence was the political-genealogical fruit of the Branwen-Matholwch alliance-marriage. At the peace-feast attempting to resolve the Welsh-Irish conflict, acclaimed king of Ireland by both sides as the political-symbolic resolution. Immediately after the acclamation, killed by his maternal half-uncle Efnisien who threw him into the fire — destroying the political-resolution and triggering the open Welsh-Irish war. The Gwern-killing is one of the most-shocking episodes of medieval Welsh literature and a foundational political-tragic-failure case-study: the political-symbolic resolution that fails through the unilateral act of a single resentful figure (Efnisien). The Gwern-foundation-failed-resolution arc parallels broader Indo-European political-tragic narratives where alliance-children become collateral damage in inter-polity violence (Trojan War cycle, Ramayana, etc.).