Mentalis

Mentalis was a war computer.

Mentalis was built by Drax at the behest of the Shadow to direct the war between Atrios and Zeos. It was discovered by the Doctor while on Zeos with Shapp, Merak, Romana and K-9. K9 was able to communicate with it and considered it an interesting conversation. However it refused to answer any inquiries about Astra, nor would it allow them access to its databanks. With the war over, it decided it would destroy everything and everyone on both sides.

Mentalis was fitted with a self-destruct mechanism if it felt threatened, this was activated when it sense the marshal of Atrios homing in to attack. The Doctor attempted to disable it, confused as to preventing this it used its own defence weapons against its command centre, destroying it. The countdown continued so the Doctor employed a time loop to prevent it. He returned later with Drax who was able to disable it completely.

Mentalis was extremely powerful and nearly indestructible, capable of defending itself as well as producing and directing war material. It was programmed to think of itself as indestructible. (DW: The Armageddon Factor)