Magnus

Magnus, also known as the War Chief, Koschei, the Master, Missy, and various other aliases, was a renegade Time Lord. He/she was considered by the Doctor to be his nemesis. Magnus was responsible for several of the Doctor's regenerations.

Incarnations

 * First - This incarnation used the title of Magistrate.
 * Tenth - This incarnation went by the title of War Chief.
 * Eleventh - This incarnation used the name Felix Kriegslieter.
 * Twelfth - This incarnation went by the name Koschei.
 * Thirteenth -This incarnation went through several stolen bodies in an attempt to circumvent the regeneration limit.
 * Fourteenth - The first incarnation of the regeneration cycle granted by the Tzun. It didn't last.
 * Fifteenth - Freed from the Eye of Harmony, this incarnation impersonated the Doctor.
 * Sixteenth - Resurrected by the Time Lords, this incarnation resembled a child.
 * Seventeenth - This incarnation disguised himself as Professor Yana, his disguise so convincing even he forgot his true identity.
 * Eighteenth - This incarnation took the alias of Harold Saxon.
 * Nineteenth - The Master's first female incarnation. She went by Missy.