Morgan le Fay was an enchantress.  She was the youngest of Arthur's half sisters, the daughter of Arthur's mother Igraine.  Merlin took Morgan in as his student and was captivated by her beauty
as well as her extraordinary abilities.  Morgan was associated with healing and was one of the Queens who took the dying Arthur by barge to Avalon to be healed after he was wounded in the Battle of Camlan.  Morgan claimed she could heal Arthur if he would stay with her for a long time.

Morgan le Fay was married to King Uriens of Gorre.  She was mother to Mordred and Yvain.  Yvain  was very loyal to Arthur and this made Morgan dislike him due to the hatred of her stepbrother.  Morgan was also the one who took the scabbard from Arthur and replaced it with an identical sword she had made.  The true sword ended up in the hands of Accolon, one of Morgan's lovers.  Arthur fought Accolon not realizing he did not have the true Excalibur.  When Arthur found out about the deception of his own half sister, he swore he would never forgive her.