Stefan is Sophie and Agatha's biological father and the widower of Vanessa. He married Honora after her husband's death. In the first book Sophie suspects he married Honora to inherit her two boys, however it is in the third book it is revealed that Vanessa suspects he is the biological father of those boys as well, making them the possible half-siblings of protagonists Sophie and Agatha.
Stefan is very handsome and popular among most of the villagers in Gavaldon. He is especially highly regarded by the village elders, so much so that although the elders intended to kill Callis as a witch after her interference led to Stefan being forced to marry Vanessa, Stefan's plea for mercy led to them deciding to allow Callis to live, although as an outcast on the edge of Gavaldon.
Sophie believes that her father doesn't care for her at all, and expects that he won't mind when she enters the School for Good and Evil. But, at the beginning of the second book, A World Without Princes, Stefan begs Agatha to keep Sophie safe when death warrants are posted for Sophie, demanding she be handed over to an unspecified enemy. Moreover, when Agatha is back in Gavaldon early in the third book, The Last Ever After, Stefan wants to kill Agatha, because he believes she let Sophie die. It is only when he learns that Sophie is still alive, and that Agatha wants to save her, that he relents.
Near the end of The Last Ever After, Stefan weeps and embraces both Sophie and Agatha. Although he doesn't learn that they are both his daughters, he states that Sophie meant more to him than anyone, and he felt, because of her friendship for Agatha that Agatha was like his daughter, too. However, he is heartbroken when the girls reveal that they are returning to the fairy tale world. Sophie encourages him to appreciate his life with Honora and her two sons before the barrier that separates their worlds rises once more. His last image of Sophie is of her smiling while saying he will have the family he deserves with his new wife and sons, although he sobs plaintively for Sophie before they are parted.