The central character in Frindle is Nick Allen, the fifth grader who invents the word "frindle." Nick is intelligent and extremely creative, the innovative mind who engineers elaborate pranks in third and fourth grades. Some might consider him a bit of a troublemaker.
Another central character in the book is Nick's fifth grade teacher, Mrs. Granger. Mrs. Granger has the reputation of being a tough teacher. She has been teaching at Lincoln Elementary School for years, and is a stickler for proper language use. Mrs. Granger is stern, but not mean. She decides to play the villain when Nick instigates his fifth grade disruption with the word "frindle," but deep inside she is respectful of the boy's intelligence and daring.
Miss Deaver is Nick's third grade teacher. She is young, and new to teaching, and is perhaps a little gullible in playing along with Nick's innovations.
Mrs. Avery is Nick's fourth grade teacher. She looks like a hawk, and tries to keep order in her classroom, but Nick manages to outwit her.
James Allen is Nick's older brother. He is in college when Nick is in fifth grade, and has set a high academic standard for his little brother.
Judy Morgan is a reporter for the local newspaper. She is efficient and has a nose for interesting news.
Mrs. Chatham is the principal at Lincoln Elementary. She is a large woman who tolerates no nonsense at her school.
Mrs. Allen is Nick's Mom. She sets firm rules for her children's behavior, but is also fun-loving and defends Nick when he gets in trouble for pushing the use of the word "frindle."
Mr. Allen is Nick's Dad. He is more retiring that Mrs. Allen, and is uncomfortable with all the commotion his son has started.
Bud Lawrence is a local entrepreneur who sees an opportunity in the popularity over the word "frindle" and takes steps to capitalize on it. He does take advantage of Mr. Allen's discomfort with the whole phenomenon, but he is not really a dishonest man, and he sends Nick regular royalties after gaining the rights to market "frindle" products.
Janet Fisk is a classmate of Nick who is fun-loving and more than willing to take part in Nick's shenanigans.