Her parents are usually named as Gorlois and Igerne, she was Arthur's half-sister. When her widowed mother re-married Uther Pendragon, Morgause married King Lot of Lothian and had several children - Gawain, Gaheris, Agravain and Gareth. Her sisters were Morgan le Fay and Elaine.
Morgause’s husband went to war with Arthur at the beginning of Arthur’s reign, but was defeated. Shortly after this defeat, Morgause visited Arthur in his bedchamber and conceived Mordred. (Arthur had been ignorant of Morgause’s identity, and of the fact that she was his half-sister.) Eventually, her husband was slain and all her children departed to take service at Arthur’s court. She began an affair with Lamorat, the son of King Pellinore, who was a family enemy. When her sons found her in bed with Lamorat, Gaheris killed her.
Various romances credit her with a number of affairs. The Enfaces Gauvain makes Lot her page, with whom she had a brief liaison, which resulted in the birth of Gawain.
It appears that Morgause may not have been the original name of this character, and it may indeed simply be a territorial designation, much in the same way as her husband's name Lot means 'Lothian-ruler'. This seems likely, for in Diu Crône she is referred to as Orcades or Morchades, which seems to indicate that she originally hailed from the Orkneys, which was one of Lot's kingdoms (the Latin for Orkneys, Orcades). The variant Morchades is thought to have given rise to Morgause.
In Malory, the wife of Lot is called Anna, the sister of Arthur, while in De Ortu Waluuanii Morgause is replaced again by Anna, though this time in the role given in the Enfaces Gauvain, the mother of Gawain, following a secret intrigue with her page, Lot.
In Arthour and Merlin, she is called Belisent. Her character is not named in the Vulgate and Post-Vulgate Cycles. The earliest occurrence of her name, Orcades or Morcades is found in the First Continuation of Chrétien's Perceval.