Rhiannon

Legends of Rhiannon, Welsh Goddess of the Underworld associate her with horses, particularly riding wearing a golden robe with magical birds whose singing woke the dead or brought blissful sleep to the living.

When she appeared to Pwyll, Prince of Dyfed his swiftest horses couldn't catch her. In frustration he called out and she stopped and married him. When their newborn son disappeared she was accused of eating him and sentenced to be Pwyll's gatekeeper, carrying visitors on her back as a packhorse. Later, when he was found magically in a stable she was reinstated.