The Master (Terror of the Autons)

In a physically degenerated condition and with no more regenerations left, the thirteenth incarnation of the Master attempted to find an energy source to restore himself.

Escape to Tersurus
During his prior incarnation, Susan Foreman triggered an explosion when the Master attempted to kidnap her. He exhausted his regeneration cycle recovering from the injuries sustained in the explosion on the planet Tersurus (EDA: Legacy of the Daleks). Here, the Time Lord Chancellor Goth found the Master, in a wasted condition. The Master had by this time reached the end of his regeneration cycle and had turned into an animate though rotting corpse. (DW: The Deadly Assassin)

On Gallifrey
The Master made Goth, in line for the position of Lord President of the High Council of Time Lords, into a helpless slave. He also took over the mind of Solis, one of the Chancellory Guard. With a telepathic summons and a vision of the future created by the Matrix, Master lured the Doctor to Gallifrey to prevent the murder of the then-serving Lord President. The Doctor failed and ended up on trial for the President's murder. In the mean time, the Master casually killed a guard with his Tissue Compression Eliminator and left it for the Doctor to find like a grisly calling card.

Secretly, the Master had access to the Matrix. He also had guessed the secret of the Eye of Harmony and various artifacts left behind by Rassilon. He realised that the Eye of Harmony, a black hole, resided beneath the Panopticon and, realizing that it had immense power, believed he could use the Sash of Rassilon to protect himself from the raw power of the Eye and the destruction that unleashing it would cause. He thought that it could channel that energy to renew himself. The Doctor defeated the Master in physical combat. The Master appeared to have fallen into a crevice created by a localized earthquake. In fact, he had gained access to his TARDIS, disguised as a grandfather clock and escaped. Cardinal Borusa determined to make it look to the people of Gallifrey as if Goth had died attempting to stop the Master's evil plans. (DW: The Deadly Assassin)

On Traken
The Master repaired to the planet Traken, the center of Traken Union in a TARDIS configured into the sculpture-shaped Melkur. He set about a plan to steal the Source to restore himself. To this end, over a period of years, he won over Kassia, wife to Tremas and mother of Nyssa. Defeated once more by the Doctor and Adric, he took over the body of Tremas. (DW: The Keeper of Traken)


 * For an account of the Master's activities in Tremas' body, see separate article.