Savant is a primary character who fills the archetypal role of mentor. He is also how the children discover the existence of the Whangdoodle and Whangdoodleland, making him key to the novel’s inciting incident. 

Though Savant is an accomplished professor who recently won a Nobel Prize for his work in genetics, Savant’s primary work doesn’t have to do with his practical career. Tom asks Savant why he knows so much about the Whangdoodle, and Savant replies, “That’s because I am different. Some people consider me an eccentric. I specialize in imagination. I imagine things most people wouldn’t even dream of” (37). Savant sees imagination as an intellectual exercise and approaches it with the same rigor as genetics, telling the children, “I had to go into training. I had to stimulate and teach my mind to become aware and open to any possibility” (36). Savant becomes the educator and leader of the Potter children, imparting knowledge that prepares them for their journey and ultimately traveling with them. 

Savant is intelligent and amicable, and he doesn’t talk down to the children. By inviting them on the journey, he treats them as equals. At the same time, Savant uses his experience to help them survive various antagonistic creatures. When they face the Swamp Gaboons, for instance, he heeds the Whiffle Bird’s advice and pushes the children not to reply to the insults. Nevertheless, it is crucial for the children’s character arc that Savant prove fallible, as he does when he doubts his own imagination, forcing the children to continue on their own. Still, Savant is willing to accept help when he needs it, eventually allowing Lindy to coax him into the palace and listening to the Prock and putting on the scrappy cap. 

After aiding the Whangdoodle, Savant plans to go to Washington, DC, to help the American president deal with genetic developments. The implication is that Savant will bring integrity to the political realm. Summing up Savant’s principles, Ben tells his father, “We will have a tremendous responsibility on our hands. If we’re going to play God [by creating life] we must try to do it with honor and decency” (277). Julie Andrews implies that Savant’s imaginative nature contributes to this moral outlook.

Ben and Tom are Lindy’s older brothers, with Tom being 10 and Ben being 13. As the oldest, Ben acts maturely. When Lindy tells her mother she’s afraid to go trick-or-treating with her older brothers, her mother suggests speaking to Ben, reinforcing his characterization as a thoughtful young person. The narrator writes, “Ben was flattered that Lindy would turn to him in a time of crisis and he answered in a big-brotherly way” (21). Tom is less mature, and he and Lindy have a more stereotypical sibling relationship. They quarrel at the zoo, with Tom saying that Lindy is scared of snakes and immature for sucking her thumb. Ben, embracing his role as a voice of reason, tells them, “Cut it out, you two” (5). Yet Tom and his sister are not enemies. When he thinks a witch is besetting her at Stone House, he yells, “You leave my sister alone!” (26). Similarly, when the Splintercat kidnaps her, Tom and Ben contact Savant and assist in the rescue. Tom’s squabbles aside, Tom and Ben are mostly caring older brothers.

Although Tom and Ben are relatively flat and static characters, Andrews uses the brothers to subvert gender tropes. At one point, seeing a pair of ostensible motorbikes, the boys hop on them. Unfortunately, the bikes turn out to be dangerous Gazooks. Lindy excuses their behavior, but Savant holds them accountable. He tells Lindy, “I felt exactly that way when I was a boy […] But occasionally an angry, sensible adult showed me the error of my ways” (190). Savant indicates that boys are teachable and their behavior is modifiable.

For much of the story, the Prock is the central antagonist. Savant wants to go to Whangdoodleland and meet the Whangdoodle, but the Prock, acting as a prime minister, wants to keep Savant away. As Savant and the Potter children are good, the Prock, due to his opposition to them, appears bad. The Prock’s actions cement this characterization, as when he dispatches an array of creatures to stop the group, even sending the Splintercat to kidnap Lindy. The Prock’s appearance contributes to his apparent antagonism as well. He’s “tall and exceedingly thin” with “a long body and very long arms” (40)—vaguely humanoid, but unusual enough in appearance to be uncanny. When he leaves Savant (and, later, Lindy), he suddenly vanishes like a long, slippery snake. Although Savant at one point implies “Prock” is the name of the Prock’s species, no other characters like him appear, so the Prock becomes a creature unto himself. 

The Prock’s actions for most of the book showcase a type of stony ruthlessness. As an antagonist, the Prock is manipulative and untrustworthy. When he approaches Lindy on the street, he lies, telling her that he and Savant are friends. The deception disarms Lindy and gets her to tell him about their plans to visit Whangdoodleland. 

At the same time, the Prock isn’t deadly. He doesn’t harm Savant or the three children. When the Whiffle Bird gets hurt, the Prock cares for her. Witnessing Lindy’s tears turns him into an ally. He drops his antagonism and introduces the children to the Whangdoodle. Though he keeps his harsh diction—referring to the children as “hostages”—he helps Savant create a female Whangdoodle by pushing Savant to put on the scrappy cap. By the end, the Prock reveals himself to be a good character, contributing to the happy resolution.

The Whangdoodle is the titular creature and in many ways an embodiment of imagination. As his name indicates, he’s rather absurd, with a mishmash of traits. He has “horselike teeth,” the body of a “small pony,” and antlers that are “amazingly large and very handsome” (222). Adding to the fanciful characterization, he grows his own bedroom slippers. In keeping with his playful image, the Whangdoodle is rather jovial, as when he cheerfully greets the children. Yet the Whangdoodle can also be suspicious of people, in part because their lack of belief in Whangdoodles has caused the extinction of his fellow creatures. After telling the siblings, “Humans can’t be trusted,” he then asks, “Do you still fight over territory and so on?” (223-24), thematically linking violence to a lack of imagination and implying that such troubles do not exist in Whangdoodleland. 

The emphasis on violence in the human world indicates that the Prock was justified in wanting to keep humans away. Nevertheless, the humans help the Whangdoodle, with Savant countering his loneliness by producing a female Whangdoodle, Clarity. Indeed, the Whangdoodle is indebted to Savant for reasons besides Clarity. He tells Savant, “The only reason I was able to stay alive in those dreadful times was because I was certain that somebody, somewhere, still believed in me” (268). The implication is that the Whangdoodle is alive because of Savant’s imagination.