D84 was a unique robot, completely independent of a Super-Voc and with a high level of logical reasoning. D84 was an undercover agent disguised as a 'Dum' and placed on board Storm Mine 4 as a precaution to threats that Taren Capel would lead the robots into a revolution against humans. D84 worked alongside another agent, Poul. D84's cover was first blown by Leela who when finding a third corpse saw that D84 was in the room. To assure her he had no part in the murder he had to speak, but Leela promised to keep this a secret. The Doctor later found out from Leela that the Dum could speak and learned the robot's true purpose on board the Sandminer. The Doctor and D84 searched the ship for evidence that Taren Capel was on board and soon found his secret workshop, where he reprograms the robots to kill. Afterward, they found a deactivated robot and used it's head for an anti-robot transmitter. D84 is damaged when Taren Capel returns to his workshop and finds the doctor, but as a last act the robot bravely activates the transmitter at the cost of his own life, deactivating a killer robot and allowing the doctor enough time for his plan to work. It is unknown what happened to D84 after his "death," but it can be presumed he was either scrapped or rebuilt. (DW: The Robots of Death)
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