Theodor Fischer is the son of the village organist and the narrator of The Mysterious Stranger. He has had a standard Eseldorf upbringing and is trained to be a devout and unquestioning Christian in matters of religion. He enjoys playing and exploring the woods with his local friends Seppi Wohlmeyer and Nikolaus Bauman. At the onset of the story, Theodor is playful, a bit mischievous, and has a sense of childhood wonder. This includes an interest in the supernatural; he recalls exploring haunted sections of a castle and hearing tales from a guard about angels and demons. As such, his initial meeting with Satan leaves him unfazed. With the exception of learning about his hellish namesake, Theodor is excited about meeting the young angel and is open to any adventures on which he might lead him.

This changes as Theodor spends more time with Satan. Gradually, he finds himself drawn into Satan’s world. He and his friends abandon some of their previous playmates, believing that they pale in comparison to their angelic new friend. Theodor recalls, “They seemed so tame, after Satan; and their doings so trifling and commonplace after his adventures in antiquity and the constellations, and his miracles and meltings and explosions, and all that” (25).