Zanak

Zanak was a pleasant planet, with green fields, lush vegetation and friendly, Humanoid natives. It was quite prosperous until the reign of Queen Xanxia. The queen launched galactic wars which ultimately ended up ruining Zanak, leaving only a few nomadic tribes alive.

Later, the Captain crash-landed on Zanak in his ship, the Vantarialis. He hollowed out the planet, which, using powerful engines, could materialise around other planets and steal their mineral wealth. It would then crush the planets into compressed cores small enough to carry. The Captain ruled from a mountain fortress known as the Bridge. He, in turn, answered to Xanxia, who had recreated him in his current cyborg form. Xanxia had gutted her entire planet to provide the power needed to control the time dams that kept her body frozen in its last few seconds of life while she projected her consciousness into a new, virtually-generated body in the form of the Captain's nurse.

The Fourth Doctor visited Zanak and helped the Mentiads overthrow both the Captain and Xanxia. The Bridge was destroyed, allowing Zanak to settle in the position that had once been occupied by the planet Calufrax, its interior mass replaced by the remnants of the planets that Zanak had destroyed and the Captain had preserved as part of a plan to destroy Xanxia (with the exception of Calufrax, which had been the second segment of the Key to Time). (TV: The Pirate Planet)

Behind the scenes
No explicit narrative connection has ever been made between Zanak and Zanak IV, a planet featured in the audio story The Wreck of the Titan.