Jeremiah Maru-Stahl was a dictator on his planet; he killed half a million people during his rule.
Maru-Stahl was a steelworker who fomented a rebellion, and overthrew the ruling Imperial Family. As a result, he became a dictator. A rebellion formed to overthrow Maru-Stahl which resulted in a war known as the Hundred Day War.
Maru-Stahl was overthrown by the Eighth Doctor at the Battle of Nova Croix. Maru-Stahl became mentally unstable, and was moved to a hospital under the care of Elias Greenwood. Greenwood had no luck at improving Maru-Stahl's mental condition and called for the Doctor. The Doctor had many talks with Maru-Stahl, but they ended with him retreating more and more into himself. He was placed in confinement for the rest of his life. (PROSE: Gazing Void)