Tartarus

Tartarus was the name used by a computer created by the Zorth. It was tasked with identifying and supplying a life form who could serve as the leader of the Zorth during their war, a mission that it undertook for centuries.

In 1st century BC, Tartarus set a number of tasks for the Fifth Doctor, Tegan Jovanka, Nyssa, Cicero, Marc and Septus to see if any of them were worthy. It decided that Marc would be a good leader and prepared to take him away before learning from the Doctor that the Zorth were extinct. (AUDIO: Tartarus)