Cynhaiarn was a 5th-century saint from Wales and a member of the Powysian royal line. As a prince descended from the British king Vortigern, he was the brother of Aelhaiarn and Llwchaiarn. His religious life was connected to the traditions of Celtic Christianity, and he is identified as a disciple of Saint Beuno. He also received sponsorship from Saint Cadfan during his lifetime.