Gwen Coch (Red Gwen) was a witch who lived with the ellyllon (goblins) in the ancient hillfort at Moel Hiraddug. On days in which the fogs of Y Brenin Llwyd (The Grey King) misted the valleys, Gwen Goch would travel down from the hillfort and bring her mischief to the towns and villages about. Her favourite haunt was Rhuddlan, where she would terrorise the people, stealing children if she could get them and taking them back for her goblin friends on Moel Hiraddug.
At this time there was a priest by the name of Dafydd ap Hywel ap Madog, whose knowledge was so great that many thought him a magician, and he was constantly being called on by the people of the area for help in matters of the supernatural. It was not long, therefore, before the people of Rhuddlan called upon him to deal with Gwen Goch.
This the noble priest did. Climbing Moel Hiraddug, he made short work of the goblins. At the sight of this righteous man, they fled in terror, never to return to the place. He found Gwen Goch, cowering in the corner of the cave and demanded that she never trouble the people of the area again. Though Gwen Goch wheedled and pleaded, Dafydd pressed the evil hag and eventually secured her promise leave the poor people of Rhuddlan alone.
In some versions of this tale, Dafydd is a warrior monk, and clears out the goblin hordes through a shining blade held aloft, which sounds somewhat Hobbitesque, and perhaps was the inspiration for Bilbo's blade, Sting. In another, he is required to promise his soul to Satan to gain the promise of Gwen Goch, 'whether he be buried in a church or a churchyard'. Dafydd tricks the Devil by having himself buried in a hole in the wall of Corpus Christi Church at Tremeirchion, thus in neither the Church or the churchyard.