I can hardly ignore Gwyllyn even if I don't know how to pronounce his name.
He was a cattle-rustling king in fifth century South Wales. When King Brychan, a neighboring chieftain, refused to allow him to marry his daughter, Gwaldys, Gwyllyn raided the kingdom and kidnapped the girl. Brychan went to war, of course, but King Arthur (yeah, that King Arthur) backed Gwyllyn up, aided by Cai and Bedwyr. In the old Welsh tales, Arthur was always helping young bachelors win their true loves over the objections of the girls' grumpy old fathers.
Gwyllyn and Gwaldys were married and lived a happy life of crime, but their children were all strangely religious. The oldest, St. Cadoc, was sent by his father to be a student of the hermit St. Tatheus who courageously demanded that the bandit king return his stolen cow. The younger children, Cynidr, Bugi, and Egwine, was all saints also. Cadoc successfully persuaded his dad to give up theft and murder. The parents settled into a hermitage they built themselves, though Gwaldys eventually broke away and founded her own hermitage.
There are some cool miracles -- healing fountains and protection from floods and invasions and such -- attributed to him, but had I seen this one before I had written all this, I might not have given him any ink. According to the wikipedia, "the defeat of King Harold Godwinson at the Battle of Hastings was attributed to the vengeance of Saint Gwynllyw because he and his troops had plundered Gwynllyw's church recently while attacking the nearby kingdom of Gwent." For a cattle-rustler and kidnapper, he sure was touchy about thievery, especially when the national interest was at stake. Oh well, all Wales paid for his vengeance once the Normans were established on the island. Nice move, Gwyllyn.