An interesting extract I found in a book called "Folklore, Myths and Legends of Britain" - a Readers Digest published in 1973. I purchased the first edition on eBay and and delighted with this tattered and falling apart book, it's pages are folklore gold and it is a plethora of forgotten tales that you won't find anywhere on the web. I want to share this one with you..
"Long ago, a man called Sion Ddfydd, who lived in the hills above Abergavenny, was in league with the Devil. He had arranged with the Devil that his soul was safe as long as he was touching something rooted in the earth, and many times Satan tried to catch him and failed. In the end, because he was too evil to go to Heaven but too clever to be trapped by the Devil, he became a "Will-O'-the Wis