Branwen ferch Llŷr

In the medieval Welsh narrative preserved in manuscripts such as the Red Book of Hergest and the White Book of Rhydderch, Branwen is presented as the daughter of Llŷr and sister of Bendigeidfran (Brân) and Manawydan. Her tale in the second branch of the Mabinogi opens with a diplomatic marriage arranged between Britain and Ireland: she weds Matholwch, king of Ireland. The subsequent insult to her kin and her mistreatment in Ireland lead to a British expedition led by her brother Brân, a great battle with miraculous elements, and the story's etiological and moral consequences for inter-island relations.

The primary medieval sources and modern summaries focus on Branwen's role and fate rather than providing a detailed physical description. The tale emphasizes her status as a princess, mother (of Gwern), and the sufferer whose treatment catalyzes major events.

Branwen is not ascribed supernatural powers in the source material; her agency is social and narrative: she accepts a politically arranged marriage, bears a son (Gwern), endures abuse in the Irish court, and shows resourcefulness by taming a starling and sending it with a message across the sea to summon her brother Bendigeidfran. Her significance lies in kinship ties and the consequences of her mistreatment rather than magical abilities.