A teacher and master builder from King's City who once headed the Mason Guild. After a theater collapsed because officials had replaced the original stone with cheaper material, he left the capital and went into hiding in Border Town. Calm, sensible, and conscientious, he takes his work seriously and without unnecessary display. For a long time, like many others, he accepted the Church's teachings about witches as truth, yet what he later witnessed gradually made him question those beliefs.

In Border Town, he opens a school and teaches ordinary children rather than only the sons and daughters of nobles. Among his students are Anna and Nana Pine, and his closeness to them greatly changes his view of witches. After Nana's awakening, he resolves to protect her and tries to convince the local lord of the witches' innocence. Practical-minded, open to new ideas, and willing to take on any useful task, he proves valuable both in the classroom and at the building site.

Under Roland, Karl becomes one of the key figures responsible for the town's development. He readily takes on new projects, applies all of his experience, and helps carry out plans connected with the expansion and reconstruction of Border Town. In time, he is entrusted with overseeing construction work and eventually becomes Minister of Construction.