Deemon was an "evil genius" who served Grekk. He was left on an Earth-like planet with Grekk's sons to keep them hostile towards the planet's other inhabitants. He attempted to assassinate one of the sons of Grekk and blame the Crustians, but the First Doctor stopped him. He later reprogrammed the Mechanislaves to attack the Doctor and the prisoners who had escaped, but the Doctor bluffed him into ordering the robots to stand down, and the cockroach-like prisoner restrained him. (PROSE: The Sons of Grekk)

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