Skovox Blitzer

A Skovox Blitzer was a robot built for war, said to be among the most dangerous weapons ever created. A single Blitzer contained enough armament to destroy a planet. One came to Earth in the early 21st century and was deactivated by the Twelfth Doctor, who left it drifting in space.

They were extremely efficient killers to the extent that workers of the Nethersphere dealt with admitting their slain victims on a frequent basis. (TV: The Caretaker)