The Mechanical Hound is a robotic assassin in the novel "Fahrenheit 451" by Ray Bradbury. This robot is described as being made out of copper wire and storage batteries. Its purpose is to enforce the laws set by the government.
The Mechanical Hound was inspired by the use of dogs by firefighters in rescue operations. Whereas the purpose of rescue hounds is to locate those in need and help them, the purpose of the Mechanical Hound is to locate those who do not adhere to the rules and punish them.
The character has been likened to the Furies in ancient Greek mythology, symbolizing the government's appropriation of technological advances for its own agenda of oppression.