Sophie Amundsen - Sophie is the protagonist of Sophie's World. She is an inquisitive and spirited fourteen year old who learns just before turning fifteen that her life is the invention of Albert Knag. Sophie learns this and many other things from Alberto Knox, the philosopher who Albert Knag invented as her teacher. Sophie does not just learn from Alberto; she also questions him and shows that she has ideas of her own to implement. By the end of the story Sophie shows that she is a philosopher, because she has the ability to look at things from a different perspective and she can act on what she thinks. Sophie is friendly but not all that social. She is more given to introspection than chatting. In fact, Sophie almost forgets about her one good friend, Joanna, when she starts learning about philosophy. Sophie is critical, and she does not spare those she cares about. Her mother has to listen to much criticism from Sophie throughout the book, and Joanna and Alberto also hear a fair share. Sophie is opinionated and she is interested in saying only what she thinks.
Alberto Knox - Sophie's teacher, Alberto Knox represents the ideal philosopher. He is never quick to judge and he always thinks about what he is doing. Alberto believes passionately in philosophy, since it helps him understand that his existence is due to the mind of Albert Knag. Alberto is an excellent teacher because he forces Sophie to think things out on her own and does not make things easy for her but he also cares about her and wants her to learn.
Hilde Møller Knag - Hilde is Albert Knag's daughter and Sophie and Alberto are created for her amusement. Like Sophie, she is a deep thinker, and the philosophy in the book intrigues her deeply. Hilde is also extremely compassionate, and she feels for Sophie and Alberto while her father plays with their lives. She is independent, and proves it by giving her father a taste of his own medicine during his return from Lebanon.