Karl is a middle-age man with some white hair on his sideburns. His skin is slightly tanned due to often being on construction site.
After "Anna" was hanged for being witch Karl's world view has changed: he started doubt Church's teachings. After Nana's awakening he made up his mind to fight religious propaganda and convince lord of Border Town in witches' innocence.
Karl is open minded and ready to complete any construction project whenever Roland propose it using all his building knowledge and advice.
In King's City Karl was the head of Mason Guild. To save payment for theater construction Kingdom officials changed stone material, which led to building's collapse and death over thirty masons. As the chief mason Karl was sentenced to exile, while Mason Guild was disbanded. After leaving King's City he moved to Border Town and established local school. Unlike common practice in Kingdom of Graycastle he was teaching ordinary children. Among his students were Anna and Nana Pine.
Karl responded to mason recruitment for new city wall, hoping to save Nana and prove witches' innocence. After joyful reunion with Anna Karl asked technical requirements and voiced his doubts. To dispel his scepticism Roland demonstrated bricks bound by cement. Realising its potential he agreed to lead construction of defensive wall.
During winter and spring Karl was the busiest official of Administrative office. He was responsible for maintaining the city wall, construction of brick houses and temporary wooden sheds for serfs. When Roland returned from Longsong Stronghold he was ordered to build stilt warehouses, furnaces and public toilet in wooden sheds area. He asked prince to invite masons from the disbanded guild and received his approval.
Karl, as former head of the Mason Guild, was knowledgeable about the details and necessities in constructing buildings that were common in the Kingdom of Graycastle. This required him to be able to make precise enough measurements so that the buildings would be structurally sound.
Karl is deeply grateful to Roland for sparing the lives of Anna and Nana, as well as giving him the opportunity to be a mason again.