- You may be looking for the Silver Doctor, an automaton with the Eighth Doctor's voice created by Alfred Stahlbaum.
Being modelled on the Eighth Doctor in appearance, the puppet could also speak simple phrases with the Doctor's voice. Although the Doctor thought that the likeness was lousy, especially as far as the hair was concerned, it was sufficient to fool Mary Shelley, the Doctor's companion.
The confusion was cleared when the Doctor himself entered the room, pursued by the puppet of Mary. The Doctor and Mary managed to distract each puppet by the other puppet and get away. The puppets of the Doctor and Mary then destroyed each other.