The Watchman's Oracle was the head of a damaged Cyberman of the Cyber Legions. It came to be damaged when a Cyber Ship crashed down on the village of Klimtenburg prior to the 19th century. In the 19th century, the Watchman discovered the still-functioning Cyberman's head and it offered him knowledge in the field of technology, helping him to build a robot copy of the deceased Marie Ernhardt and put together a cybernetic body for her ill son Victor Ernhardt, among other things. While the Watchman came to consider the head his Oracle, in reality the Cyberman was manipulating him into helping the Cybermen recover. He kept it in his workshop on a plinth behind a curtain since the damage to its eyes inflicted by the crash made it extremely sensitive to light.
When the other Cybermen revived and attacked the village, the Eleventh Doctor charged Victor's Cyberman body with a lightning strike. The attack was stopped when Victor grabbed the Oracle and reconnected with the Cyber-network, sending the sudden surge of power through the network which caused the Oracle to explode, quickly followed by all of the other Cybermen. (PROSE: Plague of the Cybermen)