* Bobby Phillips: A 12-year-old boy who suddenly becomes invisible. He's curious, resourceful, and tries to navigate his new reality with humor and resilience.
* Alice Albright: Bobby's best friend and classmate. She's intelligent, compassionate, and initially skeptical but later becomes a crucial ally to Bobby.
* Mr. and Mrs. Phillips: Bobby's parents who are initially worried and confused by their son's disappearance but eventually try to understand and support him.
* Mrs. Albright: Alice's mother who is initially suspicious of Bobby's "disappearance" but eventually becomes a voice of reason and support.
* Principal Reynolds: The stern and suspicious principal of Bobby's school.
While not necessarily a "main character," the town of Pine Bluff, where the story takes place, plays a significant role in the narrative.