Morgause Fay

Morgause is among the most powerful sorcerers on Earth and an enemy of Merlin.

Biography
Morgause was the daughter of Gorlois and Igraine. Gorlois was killed by Uther Pendragon who married Igraine, producing Arthur Pendragon. Morgause was wed off to King Lot, one of Uther's allies. After Uther's death, King Lot attempted to overthrow King Arthur but was defeated.

Morgause seduced Arthur, conceiving Mordred.