Milo
Milo is perpetually bored and a poor student until he drives his toy car through the phantom tollbooth, which he builds from a kit that was sent to him anonymously. Through his adventures across the strange lands on the other side of the tollbooth, he learns to see and appreciate the things around him. Milo learns the importance of learning and realizes that knowledge is empowering.
Tock
Tock is a large watchdog with a watch on his side. He ticks and makes sure no one wastes time. Tock wants to help Milo make the most of his time. He also shows Milo how to escape the Doldrums—both literally and figuratively. He is loyal to Milo and wants to help him.
Humbug
The Humbug is a large beetle who carries a cane and is dressed in a fancy coat, striped pants, and a derby hat. He has a booming voice and an overbearing personality. The Humbug appears to be a bit of a braggart and has an inflated ego and sense of importance. He meets Milo and Tock when they arrive in Dictionopolis, and the king of Dictionopolis volunteers him to guide Milo and Tock on their travels.
King Azaz
King Azaz rules Dictionopolis and believes in the power of words. He and his brother, the Mathemagician, have banned the princesses, Rhyme and Reason, for declaring that words and numbers are of equal importance. Azaz realizes he was wrong and sends Milo to the Castle in the Air to rescue the two princesses. He is willing to welcome them back.
Mathemagician
The Mathemagician is a large man who wears a coat covered with numbers. He rules Digitopolis and believes in the power of numbers. He and his brother, King Azaz, have banned the princesses, Rhyme and Reason, for declaring that words and numbers are of equal importance. Unlike his brother, he is not eager to help them return, although this changes by the end of the novel.
Rhyme
Princess Sweet Rhyme is a gentle woman who has been forced by her brothers to live in exile in the Castle in the Air. She and her sister have been banned because of their belief that numbers and words are equally important. She believes in the power of learning, and her presence will help restore order to the kingdom.
Reason
Princess Pure Reason is a gentle woman who has been forced by her brothers to live in exile in the Castle in the Air. She and her sister have been banned because of their belief that numbers and words are equally important. She believes in the power of learning, and her presence will help restore order to the kingdom.