Er, that Skullmonkey seems familiar, doesn't he? After falling from his homeworld Klogg someday lands straight on planet Idznak, home of the Skullmonkeys (and a couple of Ynts).
Twisted as his mind is he at once comes up with a plan to get his revenge on his father Hoborg and especially his bro Klaymen, who ended Klogg's (unrighteous, but tell that to Klogg..) reign. Disguised as a Skullmonkey he manages to become ruler of this place.
With the help of his new.. helpers he creates a giant machine to destroy his former home - but one of the monkeys, Jerry-O, who saw Klogg's true self, tries to get help in time...
In the game you'll meet Klogg in the movies Intro, Evil Engine and Secret Ending, and of course in the boss-level Klogg.