Skonnos

Skonnos was a brown, dirty planet with a grey sky. (TV: The Horns of Nimon) Skonnos' nearest neighbour was the planet Aneth, home to the peace-loving Anethan people. (PROSE: Doctor Who and the Horns of Nimon)

History
The planet was ruled by the first Skonnan Empire, but it collapsed due to infighting until only the army was left. Eventually, they were then discovered by the Nimons, who bribed them with advanced technology. Though the Nimons planned to use the energy of Skonnos themselves, they were stopped by the Fourth Doctor, Romana II, K9, Seth and Teka. (TV: The Horns of Nimon)

Koschei, before he came to call himself the Master, arrived on Skonnos at the height of the first Skonnon Empire. (PROSE: The Dark Path)