Nancy Bobofit: freckled, redheaded, kleptomaniac. Percy's chief tormentor and the catalyst for the shocking events at the museum.

Grover: Percy's best friend; the only sixth-grader with acne and a wispy beard. Curly brown hair, Excused from PE because of a muscular disease in his legs.

Mr. Brunner: Percy's Latin teacher, middle-aged, in a motorized wheelchair. Thinning hair, scruffy beard. Wears a frayed tweed jacket and tells stories and jokes in class. Has a collection of Roman weapons.

Mrs. Dodds: mean math teacher, always wears a black leather jacket and dislikes Percy. At the museum she transforms into a shrivelled hag with yellow fangs and attacks Percy.