After her sister Igrayne marries Uther, Morgan goes to a nunnery, where she becomes a great sorceress, then marries Uriens of Gore.
Morgan and her ladies capture Sir Launcelot and attempt to seduce him.
Later, she steals Excalibur and gives it to her lover, Sir Accalon, instructing him to use it in his next battle, which she knows will be against Arthur.
When she learns Accalon is dead, she rides to the abbey where he lies and steals Excalibur's scabbard, which has magical protective powers, from Arthur, who chases her. But she escapes, of course.
After returning to Gore, Morgan sends an enchanted robe to Arthur in an attempt to assassinate him. Instead, Morgan's messenger is forced to wear it and immediately burns to ashes. Yikes.
Morgan kidnaps Sir Launcelot and, along with three of her ladies, attempts to seduce him. He refuses.
Then, she lays an ambush for Sir Launcelot, but is thwarted by Sir Trystram.
This prompts Morgan to kidnap Sir Trystram. She only releases him when he promises to carry a painted shield bearing a message about Launcelot and Gwenyvere's affair in an attempt to inform Arthur of it.
After Arthur is wounded at Salisbury Plain, Morgan is one of four ladies who appears on a barge and carries him away in an attempt to heal him.