The Cylinder

 was an alien weapon that had been created by a race known as the Sussyurats, who sought vengeance on the Doctor for an unspecified past defeat. After detecting reports that the Doctor was in the Generios system, the cylinder travelled there, requesting that it receive the three greatest treasures of the system as 'tribute' in three hours, reasoning that only the Doctor could accomplish such a feat. However, although the Sixth Doctor completed the task, the Cylinder ended up capturing Banto Zame instead, Banto having been posing as the Doctor. (AUDIO: The One Doctor)