Events prior to the manga
Spittledrum started out as just another goblin soldier, though perhaps of a higher rank than the usual grunts. He protested Jareth's rule, as after the events of the movie, Jareth clearly could not use his will to control the Labyrinth, and in Spittledrum's eyes, it showed a weakness. Combined with goblin prejudice, he feels that only a goblin should control the Goblin Kingdom and starts to desire total power, implying a coup just outside the gates. However, unlike Cob the Gob, Jareth makes him Mayor of Goblin City upon return from his trip to Moraine to create the ablation Moppet. Spittledrum also ends up with the discarded Moppet, taking her from a Trash Lady goblin in the Junkyard and hiding her presence from Jareth (for awhile, anyway) and the other goblins (by masking her scent as a human).
Role in the manga
Spittledrum begins as a very bigotted, very irritable goblin, frustrated that time should be taken away from his important governing duties to "babysit" Toby in the real world so the kid's wishes can be granted. He acts very hostile to Toby, as he feels only goblins should rule the Goblin Kingdom. However, this is in large part due to Jareth's mismanagement of the Kingdom as well as the Running Gag of Jareth never remembering names. When Toby becomes heir to the Labyrinth, he makes it a point to involve Spittledrum and respects him and calls him by the right name, which begins to turn Spittledrum into a grumbling, but nicer, ally. His path is contrasted with that of Candlewic, who lets his resentment lead to betrayal. Spittledrum, while being a relative jerk, has a powerful heroic moment when Mizumi takes over. After recuperating, Spittledrum becomes a more sincere ally, though he stil relies on reminding goblins of their proud heritage in order to save the Kingdom.