 Caradog is the grandson of the sea god Llŷr, the nephew of Manawydan, Branwen, Efnisien and Nisien.The Irish king Matholwch sails to Harlech to speak with Bran the Blessed, high king of the Island of the Mighty and to ask for the hand of his sister Branwen in marriage, thus forging an alliance between the two islands.Bendigeidfran agrees to Matholwch's request, but the celebrations are cut short when Efnisien, a half-brother to the children of Llŷr, brutally mutilates Matholwch's horses, angry that his permission was not sought in regards to the marriage.