Ah, Queen Anna Morgause, the most evil witch across in the Arthurian tales, and a rather confusing historical record. Known as "The Witch of Orkney" and the Queen of Lothian and the Out Isles, and has her own book, "The Queen of Air and Darkness", written by T.H. White. The sister of witches Morgan le Fay (who factors into the Arthurian tale earlier, by trying to tempt Arthur and Kay with a castle of lard); Morgause is by far the most inclined to use witchcraft in almost every interpretation of the Arthurian legends. In T.H. White's The Once and Future King, she is portrayed as being cruel and heartless, ignoring her children to amuse herself with an invisibility spell. She also beats them and manipulates them by having her side with her own Orkney faction.
Married to King Lot of Orkney, Morgause tries to garner sympathy from her sons (Gawaine, Gaheris, Gareth, and the evil Agravaine) by telling them the story of the "rape" of Queen Ygraine, her mother, by Uther Pendragon, the High King of England-although sources differ as to whether this was a rape or an act of mutual consent. She also tries to seduce almost everyone who comes into her court, including Sir Pellinore, Sir Palomides, and the old codger Sir Grummore Grummersum. Even while her sons are knights of the Round Table, they still resent Arthur and blame him for their mother's unhappiness.
Physically, Queen Morgause is described as being tall and lithe, with very long red hair, fair skin, and "green, slanting eyes." In Mary Stewart's The Last Enchantment, Queen Morgause influenced King Lot, not Arthur, to order the slaying of Mordred, the product of her union with King Arthur, who did not know at the time that Morgause was his very own half sister.
Of course, this is only legend. She is first mentioned by Geoffrey of Monmouth, in his History of the Kings of Britain, as a full sister of King Arthur and the daughter of Uther Pendragon and Queen Ygerna. She reportedly married King Lot of Orkney. She is reportedly born in A.D. 457.