Sophie’s philosophy teacher and guide, who initially maintains an air of mystery. He is passionate about educating Sophie in the ways of philosophical thought through meetings and lessons.

A UN official and author who writes the philosophy book Sophie is a part of. He is connected to the narrative through postcards addressed to his daughter.

The daughter of Major Albert Knag, who receives messages throughout the story and is linked to mysterious occurrences tied to Sophie. She shares a birthday with Sophie, connecting their stories in unique ways.

Sophie’s caring but practical mother, who becomes concerned with Sophie’s interactions with her philosophy teacher. She supports her daughter’s burgeoning interest in philosophy.

Sophie’s best friend, who engages in philosophical discussions with Sophie early in the story and assists her in planning a birthday party. She represents a slice of Sophie’s normal, day-to-day life.