The Humbug completes the trio of travelers, having been sent along as a guide by King Azaz. Resembling an enormous beetle, the Humbug has just about that much personality. He is first and foremost a braggart; the Humbug wants to be thought of as smart and important by everyone. Unfortunately, the Humbug is neither smart nor important, and it seems that the harder he tries to be perceived as such, the more foolish he appears.
It is, in fact, his shameless desire to impress that leads to his involvement in Milo's quest in the first place. When Milo and Azaz discuss the possibility of rescuing the princesses, the Humbug vainly tries to take both sides of the argument. So he unexpectedly finds himself volunteering to go along on the mission, though he would certainly prefer to stay within the safe walls of Dictionopolis.
In many ways, the Humbug acts as a contradiction to Tock. Where the watchdog is loyal, brave, and efficient, the Humbug is selfish, cowardly, and wastes a great deal of time with his blathering. Milo learns different sorts of lessons from the Humbug, but the lessons come in the form of what notto do. These lessons mostly have to do with humility, since the Humbug is the most arrogant character in all of the Lands Beyond. Milo witnesses the pitfalls of the Humbug's egotism and the benefit of avoiding such folly himself.