Edeyrn, Edyrn, Isedernus
Edern appears in French literature as Yder. Like Gwynn his character is identical to a Romano-British deity, Aeternus. He appears more often in the traditions on the Continent than the British. In The Dream of Rhonabwy he leads a Danish sable troop through Rhonabwy's dream and he is Arthur's advisor. In Erec and Enide he is called Yder fiz Nut.
Culhwch | The Legend of King Arthur