The primary character in The Phantom Tollbooth, Milo, is meant to represent the typical bored child. Milo has everything a child should want iin terms of toys and entertainment, yet he is horribly, unchangeably bored. He finds everything in his life to be completely uninteresting and has a special disdain for his schoolwork, since he thinks all of it is useless. Milo does not believe that anything he learns—numbers, words, or anything else—is applicable to everyday life.
When an anonymous friend sends Milo a huge tollbooth, he begins a journey that will change his life forever. What begins as a make-believe game (and not a very interesting one, from Milo's perspective) eventually becomes a very real journey into a wonderful fantasy world called the Lands Beyond. Structurally, Milo's journey constitutes a series of lessons from the inhabitants of this unusual land. Oddly enough, Milo is never frightened by his sudden movement between words, perhaps just another indication of how truly bored he was before the tollbooth arrived.
Through his encounters with characters in the Lands Beyond, Milo learns about imagination, using his time wisely, perspective, words, sounds, numbers and a host of other things. His ultimate goal is to find wisdom—both figuratively, through his education, and literally, by locating the missing princesses Rhyme and Reason. These themes often overlap and repeat themselves as Milo finds himself in similarly sticky situations.
Milo finds himself under the wing of many characters who impart their different lessons—sometimes intentionally and sometimes unwittingly. Milo is open and attentive to these lessons, largely because he must learn them in order to escape a situation. Throughout the book, Milo learns not only values but also how to put those values to work for himself.
When he finally returns to the real world, Milo is forever changed. He realizes that he does not need the tollbooth to travel to exotic and magical places; he only needs to look around him. The once perpetually bored Milo is suddenly inspired and enthralled by practically everything. Although he is now aware of how to travel to the Lands Beyond, he decides instead to examine the things in the more immediate world around him. Where the old Milo needed the fantasyland on the other side of the tollbooth in order to be inspired or engaged, the new Milo needs only the tools he has found through the course of the book: imagination, insight, education, and wisdom.
Milo's closest friend in the Lands Beyond, Tock, is a watchdog—a canine with a clock for a body. He spends most of his time patrolling the Doldrums, since so much time is wasted there, and decides to accompany Milo on his quest to rescue Rhyme and Reason. Tock is initially very gruff and gives Milo something of a scare when they first meet. Later, he warms up and explains that people expect watchdogs to be mean, and so Tock tries to live up to that expectation.
Being born into a long line of watchdogs, Tock believes in the value of time above all else. His purpose in life is to make sure that time is used wisely since there is, contradictorily enough, so much and yet so little of it. Tock is extremely dutiful, and it seems as if he never rests from his job and devotes all of his energies to his work as a watchdog.
When Milo first meets Tock, he is in sore need of Tock's help. The little boy has a habit of wasting time on the most useless of tasks and certainly has no appreciation of it whatsoever. Thanks to his friendship with the watchdog, however, Milo leans how important it is to use time wisely. It is important to note that Milo learns his first real lesson in the Lands Beyond when Tock saves him from the Doldrums. Without Tock's help and his newfound understanding of the value of time, it is doubtful that Milo would have completed his quest. Tock also teaches Milo about the speed of time and the ways in which it can move. Milo sees how time can fly when Tock soars out of the Castle in the Air with a number of passengers on his back.
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.