The Protector was a sophisticated computer programmed to maintain the city of its creators and ensure their welfare. The people became so dependent on the Protector that it had to maintain their existence by hooking them up to the computer and feeding them intravenously.
The Protector met Delthea, from the planet's future, who had to admit that the future, her time in which the Protector had been destroyed, was better than this. The Protector sent out a call to the Fourth Doctor, asking him to destroy it. The Doctor did so reluctantly. (PROSE: The Destroyers)