Rhiannon is an old Welsh Goddess of the earth and fertility, of horses and birds, who has links to the Underworld and who is much featured in the Mabinogion.
Rhiannon's first husband was Pwyll, who had once done a stint as King of the Underworld.
Their son Pryderi vanished the night of his birth while the new mother and the women sent to guard them slept. When they woke to find the cradle empty, they were fearful they would be punished severely for their carelessness. They devised a plan to cast the blame on the goddess Rhiannon, who was, after all, an outsider, not really one of their own people. Killing a puppy, they smeared its blood on the sleeping Rhiannon and scattered its bones around her bed. Sounding the alarm, they accused the goddess of eating her own child.
Later, after Pwyll's death, Rhiannon married Manawydan, brother of Bran and Branwen and son of Llyr, a great magician. One day, all of Dyfed turned into a wasteland, and only Rhiannon, Manawydan, Pryderi, and his wife Cigfa, were spared. Manawydan and Pryderi out hunting followed an enormous white boar into a caer, where Pryderi saw a golden bowl; when he touched it, he was enspelled. Rhiannon went after him and fell under the same spell the caer then vanished, taking them with it. She was rescued when Manawydan captured the wife of their enemy, Llwyd, who was taking revenge for the illtreatment of Gwawl.