Mechonoids, Gubbage Cones
The World That Waits, Impasse
Mechanus was a jungle planet that served as the homeworld of the Mechonoids. It was also inhabited by Gubbage Cones, and had terrific metal deposits which the Mechonoids mined.
As Steven Taylor explained, initially humans sent Mechonoids to prepare Mechanus for colonisation, but Earth got caught up in interplanetary wars such as the Human-Draconian War, and the Second and Third Dalek Wars. No one was bothered with the abandoned Mechonoids, figuring they would run down or wear out, but the Mechonoids constructed their city and repaired themselves, continuing to function (The Chase) even though the colonists never arrived. Steven Taylor crashlanded on the planet and was taken prisoner by the Mechonoids for several years, before being saved by the First Doctor and his companions as the Mechonoids and their city were destroyed by the Daleks, while the travellers escaped in a Dalek time machine and the Doctor’s TARDIS. (The Chase)