Branwen Daughter of Llŷr is a character from Welsh mythology, specifically featured in the collection known as the Mabinogion. She is the daughter of Llŷr and the sister of Bran the Blessed, a giant and king of Britain. Branwen is known for her beauty and tragic story, which revolves around her marriage to Matholwch, the king of Ireland. Her tale highlights themes of love, betrayal, and the consequences of conflict. After being mistreated by her husband, Branwen sends a message to her brother, leading to a series of events that result in war between Britain and Ireland. Her story serves as a cautionary tale about the impact of personal relationships on broader societal issues.