Morgan le Fay

Morgan le Fay (, meaning "Morgan the Fairy"), also called Morgaine, Morgan or Morgana, is a powerful sorceress in the Arthurian legend. She was King Arthur’s half-sister and enemy. In some legends she is said to have borne Arthur's child, Mordred. 
Morgan le Fay is said to have been quite powerful. She hated King Arthur even though he was her half-brother. (She is also said to have wiped out most of the Templar Knights). She is one of the main antagonistss of the Grey Griffins book series.