Lleu is the son of Arianrhod, but because of the shame surrounding his birth (his mother, Arianrhod, had claimed she was a virgin), she refuses to name him, arm him or provide his with a wife, and Lleu is raised by his uncle, Gwydion.

At that time, only a mother had the right to bestow those three things on a child, but through magic and deceit, Lleu gains a name and weapons, and a woman is created for him out of flowers, called Blodeuwedd.

However, Blodeuwedd is unfaithful to Lleu. She and her lover, the hunter Gronw Pebr, kill Lleu and he turns into an eagle destined to live between the realms of life and death for years until Gwydion rescues him and turns him back into human form.

Gwydion seeks revenge on Blodeuwedd by turning her into an owl, the bird of the night despised by all other birds, and Gronw Pebr is killed to atone for his sins against Lleu.