‘Tis the season of the witch!
Morgan Le Fay, also referred to as Morgana, Morgain, Morgaine, etc. was the famous witch/sorceress found in the King Arthur legends. Where originally she was described as the king’s half-sister (just a healer and magician), the stories twisted her character into something incredibly evil (enchantress, witch, murderer).
There are hundreds of articles and theories about her but I find the most thorough to come from the University of Rochester Camelot Project. You can read the article here: http://d.lib.rochester.edu/camelot/theme/morgan