Historical: A Saxon lord who owned land on the Welsh border during the time of the Norman conquest. He may have married a Welsh person, which is no big deal. An account of his historical deeds can be found here. It should be noted that his name means Prosperous, or wealthy, so we may guess that he was quite a successful lord.
Mythological: For me the legendary Edric is far more interesting than his historical incarnation. It is said that he fell in love with a Fairy woman, and kidnapped her. She agreed to marry him if he never made mention of her heritage; many years later he broke his oath and she vanished immediately. Edric himself died of grief.
Later stories cast Edric himself as a supernatural being. He, his wife, and his people were banished deep into the caves and mines until the wrongs done by the invading Normans were put right. They guide miners in the dark by tapping the walls where rich loads are. It is said that when England is about to go to war they can leave the mines for one day, and ride over the hills towards the enemy country, though they will only appear if the war will be serious. Sightings of him were reported in Shropshire before the Napoleonic and Crimean wars, and even as recently as 1914 and 1939.
Legends of Wild Edric's Followers began in the Shropshire lead mines, slowly spreading to Cornish tin mines and finally to the lead mines in Yorkshire after a migration of Cornish Tinners.