Carthok of Daodalus, the self-proclaimed Slaughterer of the Unworthy, was a psychopathic murderer responsible for many deaths, including those of Hannah Fry's parents. He escaped execution but his biomechanical spacecraft was damaged while doing so, and he was thus forced to land on Earth in 1672.
Stranded on Earth, Carthok posed as Sir Nikolas Valentine, a scholar, landowner, and astrologer, his craft disguised as his house. Over the next thirty years, he abducted many humans of high intelligence and drained them of their life energies to aid his ship in repairing itself. He did this by using homing beacons disguised as playing cards. These would scan each human, drawing the collective unconsciousness of his previous victims to the target, which would then teleport them to his ship.
By March 1702, Carthok had almost completed his repairs and was planning to return to slaughtering the unworthy, starting with the people of Earth, whom he had come to despise. His plans were defeated when the Fifth Doctor tricked him into marking himself with one of his beacons, and he was torn to pieces by the collective unconsciousness of his victims, urged on by Hannah Fry. (AUDIO: Phantasmagoria)