Gremlin Gus is the leader of the Gremlins and serves as a guide for Mickey. Almost like Jiminy Cricket from Pinocchio, he is the one that tells the player all the basic controls and how to do actions.
In the beginning of the game, Gremlin Gus rescues Mickey from the maniacal Mechanical Arm in the Mad Doctor's Lab in the Dark Beauty Castle. The Gremlins reside in Gremlin Village, which resembles the It's a Small World ride at Disneyland, Mickey could either help or abandon other caged Gremlins.
The Gremlins, including Gremlin Gus, will be reappearing in Epic Mickey 2: The Power of Two. They will play an especially larger role than the first game according to Warren Spector. Caged Gremlins will also reappear some with electricity blots around them that Oswald needs to turn off before Mickey can spin attack it.