Hilde Møller Knag is Albert Knag's daughter in the novel Sophie's World. Her father created Sophie and Alberto Knox in his novel as gift for Hilde; however, Hilde felt compassionate towards the characters, although they were fictional. Hilde shares the characteristic of open-mindedness and being a natural philosopher along with Sophie, which allows her to believe that Sophie existed somewhere, although she cannot explain how. It turns out to be true in a way, and Hilde initially perplexes her father for the assumption. By the end, she manages to receive a brief interaction with Sophie's world when Sophie hits her with a wrench.