The early works featuring Morgan do not elaborate her character beyond her role as a fay or magician. She became much more prominent in the later cyclical prose works such as the Lancelot-Grail and the Post-Vulgate Cycle, in which she is said to be the daughter of Arthur's mother, the Lady Igraine, and her first husband, Gorlois, Duke of Cornwall; Arthur is her half brother by Igraine and Uther Pendragon. Morgan has at least two older sisters, Elaine and Morgause, the latter of whom is the mother of Gawain and the traitor Mordred. In Sir Thomas Malory's Le Morte d'Arthur and elsewhere, she is married, unhappily, to King Urien of Gore and Ywain is her son. Though she becomes an adversary of the Round Table when Guinevere discovers her adultery with one of her husband's knights, she eventually reconciles with her brother, and even serves as one of the four enchantresses who carry the king to Avalon after his final battle at Camlann.
Morgan first appears by name in Geoffrey of Monmouth's Vita Merlini, written about 1150. Purportedly an account of the wizard Merlin's later adventures, it elaborates some episodes from Geoffrey's more famous earlier work, Historia Regum Britanniae. In the Historia, Geoffrey explains that after Arthur is seriously wounded at the Battle of Camlann, he is taken off to Avalon, the Isle of Apples, to be healed. In the Vita Merlini he describes this island in more detail and names "Morgen" as the chief of nine magical sisters who dwell there. Morgan retains this role as Arthur's otherworldly healer in much later literature.
Before the cyclical Old French romances, appearances of Morgan are few. Chrétien de Troyes mentions her in his first romance Erec and Enide, completed around 1170; he says one guest at the titular characters' wedding, a certain Guigomar, lord of the Isle of Avalon, is a friend of Morgan. She is later mentioned in the same poem when Arthur provides a wounded Erec with a healing balm made by his sister Morgan; this episode both affirms her early role as a healer and provides the first mention of Morgan as Arthur's sister. Chrétien again refers to Morgan as a great healer in his later romance Yvain, the Knight of the Lion, in an episode in which two ladies restore the maddened hero to his senses with a concoction provided by Morgan. However, it should be noted that while Modron is the mother of Owain in Welsh literature, and Morgan would be assigned this role in later French literature, this first continental association between Ywain and Morgan does not imply they are son and mother.
Thomas Malory mostly follows the portrayal of Morgan in the Vulgate and Post-Vulgate Cycles in his book Le Morte d'Arthur, though he expands her role in some cases. Through magic and mortal means, she tries to arrange Arthur's downfall, most famously when she arranges for her lover Accolon to obtain the sword Excalibur and use it against Arthur in single combat. Failing in this, Morgan throws Excalibur's protective scabbard into a lake.
The Fay turns up throughout the High and Late Middle Ages, generally in works related to the cycles of Arthur or Charlemagne. At the end of Sir Gawain and the Green Knight, it is revealed that the entire supernatural episode has been instigated by Morgan as a test for Arthur and his knights, and to frighten Guinevere. In the legends of Charlemagne she is most famous for her association with Ogier the Dane, whom she takes to her mystical island palace to be her lover. In the chanson de geste of Huon de Bordeaux, Morgan is the mother of the fairy king Oberon by none other than Julius Caesar.
Starting in the later 20th century, however, some feminists adopted Morgan as a representation of female power; in this context she is sometimes connected to interpretations of Celtic feminine spirituality. Such is the case in Marion Zimmer Bradley's The Mists of Avalon, which presents a different view of Morgaine's opposition to Arthur, her actions stemming from her fight to preserve the native pagan religion against what she sees as the treachery and oppression of Christianity.
In John Boorman's 1981 film Excalibur (in which she is played by Helen Mirren), Morgan takes up one of her traditional roles as Merlin's student, though her competition with her mentor assumes a new prominence in the film. In the 1998 made-for-television movie Merlin (where she is played by Helena Bonham Carter), Morgan is a hapless pawn of Queen Mab. She appears in Roger Zelazny's short story "The Last Defender of Camelot," helping an immortal Lancelot fight an age-crazed Merlin. She has been widely portrayed in comic books, for example Treasures of Britain (comic) by Simon Bisley, where she helps the hero Slaine recover her brother's lost artifacts. She has also appeared in comics from the two main comic book publishers in the United States: In DC Comics, "Morgaine le Fey" is a villainess who has battled The Demon and Wonder Woman, while Marvel Comics has long featured "Morgan le Fay" as one of their biggest female threats, with notable appearances in comics starring Spider-Woman and The Avengers.
She appears as the character Morgan le Fay in the anime film Oh My Goddess!, and showed up on the television series Stargate SG-1 as an ascended Ancient, who assists the characters in their search for a weapon left behind by Merlin (in Stargate continuity, another Ancient), and returned in Stargate: The Ark of Truth to defeat the team's main antagonist at the time, Adria. In 2006 she appeared in the middle-grade novel The Revenge of the Shadow King. Nancy Springer's I Am Morgan le Fay is told from her perspective, while she becomes a major antagonist in the Christian fantasy book series Dragons in Our Midst. She is mentioned prominently in the Magic Tree House series by Mary Pope Osborne as a "good" character who serves as the librarian of Camelot.
Poul Anderson used her in Three Hearts and Three Lions, based on the Ogier the Dane story. In Anderson's version, a modern Dane finds that he is the reincarnation of Ogier, and Morgan tries unsuccessfully to seduce him once again; he is tempted but resists her charms and sticks to his quest. She is clearly on the side of the villains in the ongoing struggle, but is still given a rather sympathetic treatment (she has an overt interest in luring Ogier away to her island, but also seems quite a bit genuinely in love with him, and is truly saddened by his rejection).
In the 2008 BBC Series Merlin, Morgana (played by Katie McGrath) is depicted as the orphaned ward of Uther Pendragon and is yet to be revealed as a sorceress. However, in a character bio video on the BBC Merlin website it is suggested that she "has an inkling of some magical power within herself.