The Pig was one of the twelve commanders of the Munificent Army of Peking. It was later known as Mr Sin.
The Peking Homunculi were created by 50th century artisans. Their first master named the commanders after the animals who visited the Buddha, and each contained a component from the animal they represented. (AUDIO: In the Year of the Cat) The "Pig" had the cerebral cortex of a real pig. (TV: The Talons of Weng-Chiang) The Pig was taken from the army, (AUDIO: In the Year of the Cat) and during the 51st century came into the possession of Magnus Greel. The war criminal and the knife-wielding automaton travelled back in time to the 19th century. (TV: The Talons of Weng-Chiang)
During the final battle between the Doctor and Greel, Mr Sin, whom Greel had unwisely allowed access to a laser rifle, became trigger-happy and fired at anyone who moved, including Greel's men and Greel himself. The Doctor finally threw it to the ground and tore out its fuse. (TV: The Talons of Weng-Chiang)