Morgaine

Morgaine or Morgan was the powerful sorceress who did battle with King Arthur and Merlin in Camelot, and the mother of Mordred. One account suggested that she was one of many emanations of the interdimensional Guardian of Magic, Morgwen. One text claimed she was an alternative equivalent of the Master.

Enemy of Merlin
After the Guardian of Magic, Morgwen, was trapped inside the Druse in the void between worlds her dreams leaked out into other dimensions. One of the sorceresses thus created was the Morgaine faced by the Seventh Doctor. (PROSE: Legends of Camelot) In actuality, she was not human, but the Battle-Queen of the S'rax; she came to Earth having detected strange energies around King Arthur, actually the result of his having been delivered by the Eighth Doctor, and was fascinated to see that Arthur's knights had far more advanced weaponry than any of his contemporaries, which had been gifted to them by Merlin.

Prior to Arthur's courtship and marriage with Guinevere, Arthur had a passionate affair with Morgaine. However, she refused to marry him, not intending to settle down with "any one male". Despite this refusal, she subsequently felt betrayed when Arthur married Guinevere, and stayed on Earth to declare war on Camelot alongside their son Mordred. The two and their Knight Commander leading knights with advanced weaponry and the capability to travel between dimensions against them. "Merlin", by then impersonated by the Doctor (PROSE: One Fateful Knight) at a point later than the Seventh Doctor, (TV: Battlefield) who may have been the Eighth Doctor (PROSE: One Fateful Knight) or a later incarnation, (PROSE: Battlefield) opposed her but was unable to stop Mordred killing Arthur at the Battle of Camlann. Morgaine believed that she had trapped "Merlin" in "the ice caves" but that he had eventually escaped. (TV: Battlefield)

According to one book, the Merlin Doctor was thus trapped within the ice caves "for eternity". (PROSE: The Monster Vault) In truth, however, the Merlin she had trapped was not the Doctor, but the other Time Lord who had impersonated Merlin before the Doctor's arrival; seeking to frame the Doctor as a traitor, he had exploited his TARDIS's chameleon circuit to make himself look like the Doctor. She placed him in suspended animation, conscious but immobile and unaging, and trapped him in the Arctic Desert forever. (PROSE: One Fateful Knight)

Some natural historians granted access to TARDIS information system would later claim these events actually occurred within an alternative universe, which they claimed was a world of magic instead of science. Instead of the Time Lords, the people of Gallifrey were the Magic Lords and had fought The Destroyers, instead of the Great Vampire. Morgaine was this universe's equivalent of the Master. The Merlin Doctor, meanwhile, was undergoing an exile on Earth that placed him within Arthur's court. Hunting for Excalibur for twelve centuries, she found it had been taken to the Seventh Doctor's universe and traveled to it with her knights, her son, and an enchained Destroyer. However, the Thirteenth Doctor refused to comment on whether the idea these events were an alternate universe were correct; she merely noted that some of the ideas had by the historians were "a bit daft" while others were very clever. (PROSE: The Monster Vault)

Encounter with the Seventh Doctor
Morgaine was attracted to 1997 Earth by the Mandragora Helix. (COMIC: Distractions)

After crossing to Carbury, England, Mordred created a meeting point, allowing Morgaine to follow him across the realities. They then set out to prevent Ancelyn and the Seventh Doctor (Merlin in her universe) from possessing Excalibur. She unleashed the Destroyer to help, but it was defeated. Morgaine made a final attempt at victory by unleashing a nuclear weapon from a nearby missile convoy, but the Doctor convinced her that this was a dishonourable form of warfare and she surrendered. Morgaine and Mordred were taken prisoner by UNIT. (TV: Battlefield)

Personality
Morgaine was ruthless, willing to sacrifice almost anything, including her son Mordred, to achieve her ends. Despite this, she had a strong sense of honour. She became enraged when, by reading a tombstone, she discovered that Mordred, had misled them and they had fought on the enemy's soil without proper respect for the dead. She had incredible powers, being able to control people and cure blindness. (TV: Battlefield)

Behind the scenes

 * In the real world, she is sometimes known as "Morgan le Fay", "Morgain", or "Morgana". She was a sorceress of Arthurian legend often described as the half-sister of King Arthur. In the legends, it was Morgan's sister Morgause who was the mother of Mordred by an incestuous affair with Arthur, but Morgan and Morgause are often conflated in later retellings.
 * Jean Marsh also played Morgan le Fay in the 1989 adaptation of A Connecticut Yankee in King Arthur's Court. She also previously appeared in Doctor Who as Joanna in The Crusade and Sara Kingdom in The Daleks' Master Plan.
 * She was played by Jenny Agutter in The Twilight Zone.