In most Arthurian literature, Morgause is the wife of King Lot (who launches a failed rebellion early in Arthur’s reign). She is also a close relative of Arthur, usually either his half-sister or aunt from his mother’s side.
In novels where Morgause has an important role, she is usually a sorceress (The Once and Future King, Hawk of May, The Mists of Avalon). She is Arthur’s enemy, and plots to usurp Arthur’s throne for one of her sons.
In many Arthurian works, she is also depicted as the mother of Arthur’s son Mordred.
Morgause is the mother of several sons with King Lot, who are often collectively referred to as the Orkney brothers (since they hail from Orkney). Her sons with Lot are: Gawain, Agravaine, Gareth, and Garehis. They all join King Arthur’s court.
Morgause is almost never depicted in a positive light. For example, she is introduced in the second book of The Once and Future King while skinning her pet cat in an attempt to cast a spell.