Rhiannon (possibly derived from a Pagan goddess Rigantona [Great-or sacred- Queen]) is a horse goddess reminiscent of Epona from Gualish religion. She's the daughter of Hefeydd the Old. She was married to Pwyll then to Manawydan. She was queen after marrying Pwyll.
Pwyll first met Rhiannon when she appeared as a beautiful woman dressed in gold and riding a white horse. Pwyll sent his horsemen after her, but she was too fast. In fact, she was riding no faster than Pwyll and his knights; her horse's swiftness was a mirage she created for Pwyll's and her benefit. After three days, he finally chased her himself. When he spoke, asking her to stop, Rhiannon told him she would rather marry him than the man who was being forced upon her, Gwawl. She made a tryst with Pwyll and after a year from that day, he won her from Gwawl by following Rhiannon's advice to trick Gwawl into climbing into a magic bag that Rhiannon had given to Pwyll, striking an agreement to free him in exchange for Rhiannon.
Rhiannon gave birth to a son after three years of their rule; however, on the night of the birth, the child disappeared while in the care of six of Rhiannon's ladies-in-waiting. They feared that they would be put to death, and to avoid any blame, smeared blood from a puppy on the sleeping Rhiannon, and lay its bones around her bed. Pwyll's counselors imposed a penance on Rhiannon for her crime, to remain in the court of Arberth for seven years, and to sit every day near a horse-block outside the gate telling her story to all that passed. In addition, she was to carry any willing guest to the court on her back.
The child appeared outside a stable of Teyrnon, whose mares had just given birth but the foals had disappeared. Teyrnon had been watching his stables when he saw a mysterious beast coming to take the foal; Teyrnon stopped the beast by cutting off its arm at the elbow, and found the child outside the stable. He and his wife adopted him. The child grew to adulthood in only seven years and was given the foal which had led Teyrnon to the stable. Teyrnon realized who the child was and returned him to Pwyll and Rhiannon, who named him Pryderi (care).
Pryderi married Cigfa and became Prince of Dyfed after his father died. He then invited Manawydan (his stepfather) to live with him in Dyfed. Soon, Dyfed turned into a barren wasteland and only Rhiannon, Pryderi, Cigfa and Manawydan survived. Manawydan and Pryderi, while out hunting, saw a white boar which they followed. Pryderi and his mother, Rhiannon, touched a golden bowl that the boar led them to and became enchanted. Manawydan and Cigfa were unable to help them until they captured a mouse which was actually the wife of Llwyd, Rhiannon's enemy (seeking revenge for her treatment of Gwawl), and the spell was lifted.
In some versions of the legend, Rhiannon was the Celtic goddess who later became Vivienne, best known as the Lady of the Lake. She was the Celtic goddess who gave Arthur the sword Excalibur, empowering him to become King in the legends of Camelot.
She represents noble traits and forgiveness because she forgives the man who took her infant child and those who sentenced her to spend years of her life carrying people to the castle.
She's a very caring and forgiving person, a good queen. After her honor was restored she instantly forgave the people who took her kid and made her suffer for it. She was so courageous that only very few people accepted her offer to carry them.
