The Warden

The Warden was a tentacled creature that controlled the atmosphere and gravitational levels on the Moon in 1878. Captain Richard Haliwell and Emily Boyes-Dennison were captured by its robotic servants and forced to take a few daring tests.

The Fifth Doctor and Turlough tried to reason with it to release the gravitational pull and let the ships leave, including the Phiadorans. They soon realised that, while it continued to obey its original orders, whether out of habit or deliberate conditioning, it apparently wanted to die after being abandoned for so long. In a flurry of bullets that cut off the power to the Warden's life-support systems, it was killed. (PROSE:  Imperial Moon)