Morgaine

"Do not stand against me this time...for your soul's sake."

- Morgaine, to the Doctor

Morgaine, also known as The Sunkiller, Dominator of the Thirteen Worlds, and Battle Queen of the S'rax, was a powerful sorceress from another dimension, who did battle with King Arthur and Merlin.

Morgaine had a strong sense of honor. She became enraged when, by reading a tombstone, she discovered her son, Mordred, had mislead 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.

Mordred, with the Knight Commander, lead Morgaine's forces: knights with advanced weaponry and the capability to travel between dimensions.

Morgaine had sealed a future version of the Doctor into the ice caves for all eternity but he escaped. She had been waiting twelve centuries to face him again.

Behind the scenes
In the real world, she is sometimes known as Morgan le Fay, Morgain, or Morgana. She was a sorceress of Arthurian legends, and believed to be the half sister of King Arthur.