Morgaine

Morgaine was a powerful sorceress from another dimension, who did battle with King Arthur and the Doctor.

In Arthur's World
Morgaine was an enemy of King Arthur and the Twelfth Doctor, who was called Merlin by everyone. Along with her son Mordred, she led her army of Cybermen, who were the converted people of Camelot. (TV: Robots of the Round Table) King Arthur was killed, but the Doctor defeated her army and sent Mordred into the future by the Doctor, who afterwards tells Morgaine she must "go the long way round". (TV: The Battle of Camlann)

In Our Universe
Mordred created a meeting point many years after his crossing to Carbury, England, allowing an older 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 had a strong sense of honour. She became enraged when, by reading a tombstone, she discovered her son, 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.