Morgan le Fay, alternatively known as Morgan le Faye, Morgane, Morgaine, Morgana and other names, is a powerful sorceress in the Arthurian legend. 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 becomes an antagonist to King Arthur and Queen Guinevere.
In Poul Anderson's Three Hearts and Three Lions le Fay's magic brings Holger Carlsen to a world based on the Carolingian cycle where he battles the forces of Faerie in a war of Law vs. Chaos. She attempts to seduce him but Holger rejects her advances because he had fallen in love with Alianora.
After Holger accepted Alianora's rejection of his love, he guested with her and her family and that evening invited them to Gerold's tavern. When the group approach it in the fading light, they saw that The Old Phoenix inn had replaced the tavern and Morgan le Fay was inside the taproom waiting for Holger. A flash of jealousy passed through Alianora but Holger pointed out that she wished to remain with Theodo, her husband, leaving him free to pursue other relationships. However, he also said that while le Fay looked seductive, he did not trust her and so would not succumb to her wiles. Nevertheless, Holger was the only one to enter The Old Phoenix while Alianora and her family stayed outside and watched the door close. They then returned to their home.