Cob is a minor character in the Return to Labyrinth series.
Events prior to the manga
Cob the Gob was banished a long time ago from the Labyrinth for being a "traitor". The crimes are not specified, but given his personality, sharing the by-now usual "goblins are superior" attitude, one can guess a coup was attempted and failed miserably.
Jareth used him as a pawn despite his exile, however, and Cob was ordered to protect a vital object of the Labyrinth's power.