The K1 Robot, also known as the Giant Robot and usually referred to simply as "the robot", is one of the two main antagonists of the Doctor Who story "Robot", the other being Hilda Winters.
The K1 Robot was an experimental robot made of a living metal, constructed by Professor Kettlewell at the Think Tank research centre. Its original intention was to replace human workers in difficult and dangerous tasks. Kettlewell's employer Hilda Winters and her assistant Arnold Jellicoe were the heads of the Scientific Reform Society, a far right group who believed the world should be run by scientists such as themselves. They convinced Kettlewell to help them use the K1 to achieve their aims. Although the K1 had been programmed with the prime directive to serve humanity and never harm it, Kettlewell helped reprogram it to believe it was allowed to kill anyone they referred to as an "enemy of humanity".
The K1 thus carried out a number of raids on scientific research establishments, stealing the plans and components needed to construct a disintegrator gun and killing a number of guards. Despite this, when ordered to kill Sarah after she trespassed at the Think Tank, it refused, since its programming had been reset to standard. Sarah sympathized with the apparent pain it felt at the contradiction. The robot then raided the home of cabinet minister Joseph Chambers, killing him, using the disintegrator gun to blast open his safe and stealing the codes needed to prime the world's nuclear missiles: Miss Winters planned to use these to blackmail the world's governments into turning over power to them.
The K1 attacked the Doctor when he turned up at Kettlewell's house, nearly killing him, but was stopped by Sarah and fled when UNIT arrived. However, he helped capture Sarah when she spied on a Scientific Reform Society meeting and stood guard at the Think Tank bunker when UNIT arrived, using the disintegrator gun. During the confusion of Sarah, Harry and a reformed Kettlewell escaping the bunker at the same time the Doctor tried to get inside, the robot accidentally killed Kettlewell, which caused it to collapse in shock.
UNIT managed to apprehend Winters and Jellicoe but the K1 shut itself in the bunker with Sarah and started the countdown to launch all the world's nuclear missiles: He believed this was Kettlewell's intention and now considered humanity corrupt and not worthy of survival aside from Sarah, the only person to show it kindness. It planned to wipe them out and repopulate the world with machines like itself. However, the plan was thwarted when the world powers activated the failsafe procedure.
As the K1 exited the bunker, the Brigadier tried to destroy it with the disintegrator gun but this caused it to grow in size and rampage around the countryside. However, the Doctor and Harry had managed to develop a metal virus, which Kettlewell had discovered would destroy the living metal, and sprayed it over the K1. The fast acting solution caused the robot to shrink and crumble to dust.