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.
Role in the manga
In the interim, Cob has been living in the sewers of the human urban landscape, collecting multiple electronic objects. Cob expresses a certain admiration for human ingenuity, creating power despite a lack of magic, but ultimately criticizes scientific pursuits as less powerful than goblin magic.
Cob still plots to defeat Jareth, having not learned his lesson, and assuming that a de-powered Jareth will be easier to defeat. However, Cob is unable to control the powerful object effectively and a furious Jareth punishes Cob by turning him into a maggot-like creature and forcing him to flee from his beloved electronic toy robot "pet".
Later, when Toby is thrown into an Oubliette, we see this maggot-like creature along with other "forgotten" goblin shadows, where one loses one's identity the longer one remains in one. Whether he was restored upon the victory over the Moraine takeover is not readily apparent.