Karl is a business management major attending a university in Munich, Germany. He has spent most of his life being bounced around between different foster families, but finally settles down with the Neumans, who love him and treat him as though he is their very own son. He knows his real father is the former business tycoon, Hans Schuwald, but is fearful to confess in the thought that Schuwald may believe he's only after him for his money. Because of this, he wants to try and get close to Schuwald in hopes that he will begin to like him, then will be more accepting if he tells him the truth.
Karl executes his plan by applying for a job involving Schuwald; once a week he will come in and read Latin to him. Schuwald has five readers for every week day, and Karl is the "Tuesday Boy." Much to his dismay, Schuwald treats him cruelly, often yelling at him because he believes his Latin isn't nearly proficient enough. Lotte Frank, a student who also works for Schuwald (not as a reader though as he only allows male students to occupy such positions), sees how harshly he's treating Karl, and befriends him, assuring him that he's stern like that with all of his readers.
Lotte tells Karl that every night around midnight, Schuwald, whose title as the "Vampire of Bavaria" seems especially appropriate in this instance, goes out for a walk. She invites him to come along with her and follow him, to which he agrees. They discover that Schuwald goes out to visit the former prostitute Blue Sophie in a nearby red light district. Sophie is currently using the alias of Margot Langer (the alias used by Karl's mother when she was in a relationship with Schuwald), and Schuwald, who still feels guilty about leaving his beloved Margot, showers Blue Sophie with money, despite being fully aware that she's just a fake and the real one is dead; it gives him a sense of relief.
Karl and Lotte confront Sophie, infuriated by the fact that she's using the name of Karl's dead mother. Picking up on the implication that this means Karl is Schuwald's son, she laughs and tells him that he's not the only student who claims he is. Baffled, Karl demands she give him information about this imposter posing as his mother's son. He and Lotte find out that this young man is Schuwald's "Thursday Boy" before departing for the night
Lotte begins to investigate and gather information about this young man, who she discovers is Edmund Farren, a philosophy major. The two plan to confront Farren after one of his classes, but discover that he neglected to show up at school, so they decide to pay a visit to his dorm room. When he refuses to open the door, they enter by force and are surprised to find him hanging. He left a note on his desk saying, "I can no longer continue to deceive."
The two report the incident to the school, and the faculty handles the situation from there. While sitting on a bench, they are approached by Lotte's handsome friend, who is Schuwald's "Friday Boy." It is then that Karl meets Johan Liebert, a law major enrolled in the university.
Johan quickly gets close to Karl, and gets Karl to reveal the details of his past to him, as well as the fact that he is
Schuwald's legitimate child. Johan tutors Karl in Latin to help him improve when he reads to Schuwald, and he shows drastic improvement. When Schuwald comments on this, Karl admits that he's currently being tutored by Johan. Schuwald begins to talk about how perfect is, and when Karl asks him what he would do if Johan was his son, he smiles. This comes as really discouraging to Karl; he decides that he really has no wish to reveal his true identity to Schuwald anymore and no longer will continue as one of his readers. Johan asks him if he has any sort of physical evidence that can prove he's Schuwald's son, to which he responds yes, and then allows Johan to hold onto that evidence.
At this point, the viewer is inclined to think that Johan is going to pass himself off as Schuwald's son, but that is not the case. Instead, Johan secretly shows this evidence to Schuwald, who gives Karl one last call, asking him to read something in Latin to him because he's very sad that Karl's no longer going to be one of his readers. Karl begins to choke up and cry about halfway through reading, and Schuwald hangs up, only to come through the door to his room a moment later. Now, both members of the reunited family are crying.
At this point, Karl is acknowledged as Schuwald's son, and spends a lot of time with him as Schuwald has now decided to enter the world of business again, which will prove to have heavy impacts on the economy of all of Europe. Because of Johan's 'kindness' he's shown to the family and his efficiency as an individual, Schuwald employs him as his secretary. At the book donation ceremony, Johan's original plan is to have Schuwald disposed of, giving him rule over Europe's economy. However, after coming across The Nameless Monster his plans change and he burns all of the books instead. During this time, Karl is sent back to the estate to "retriever some papers" for Schuwald, but actually finds a report intentionally left for him regarding Helenka. After the books are burned and Johan disappears, Karl passes on a message to Kenzo Tenma from Schuwald that Anna (Viera Černá) is still alive and the last he knew was in Prague.
Karl appears time to time following this, and at the end of the series is seen informing Schuwald of Tenma's whereabouts, to which he says he hopes to meet him again someday.
Karl is a kind and gentle young adult who always thinks of how other people would feel regarding his decisions. Just before he is recognised by Schuwald as his son, he is ready to accept his foster parents' offer to offically adopt him so that he can repay his foster parents' kindness and make them happy.
He is also a very sentimental young man who has always wished to 'go home' at night to his true family, as inspired by his frequent excursions on rooftops during twilight just to watch, while the darkness is consuming the day light, all of the homes with the members of their family going home after school or work turning on one by one.
Apart from that, he is seen to be a very understanding person, yet because he seems to be as clean as a whistle and avoids doing anything bad, like Kenzo Tenma, he can't quite make sense of those who would do the opposite. When Weber asks him if he believes Johan did all those terrible things, he just says he still does not have a full grasp of the whole happening.
Karl's relationship with Johan was characterized by the similarity of their circumstances, and he was considered by Karl to be a friend that he trusted "like no other person". Their seeming friendship would arise out of the shared context of their status as students at the University of Munich and as Latin readers of Hans Georg Schuwald, as well as their mutual connection to Lotte Frank, who introduced the two to each other. Thereafter, Johan made a conscious effort to connect with Karl and, resultantly, Karl opened up to him on his past one evening, describing his childhood as an orphan in foster care in great detail and revealing his knowledge that Hans Georg Schuwald was his actual biological father. Johan, apparently deeply moved by Karl's story on account of his own tumultuous past as an orphan, was emotionally affected enough that he began to cry, though whether or not these were "crocodile tears" designed to arouse Neuman's sympathies is left unclear. However, Johan's charisma would indeed serve to attract Karl as it did many others, and the two would form a seemingly special bond.
Later, it was Johan Liebert who encouraged Karl to reveal his lineage to Schuwald as Karl contemplated abandoning any idea of reconciling with his father and, when he was unable to convince Karl to do so, was left in the safekeeping of Karl's evidence of his claim: the lucky rabbit's foot that Schuwald had given to his late mother, who had then passed on the heirloom to their son. Johan then delivered this evidence to Schuwald himself, explaining its significance on Karl's behalf, and was thereby responsible for the reunion of Schuwald and Karl - an act that both held with such appreciation that Johan was appointed as Schuwald's personal secretary and given custodianship over the business and financial affairs of Schuwald's holdings; he would thereafter be found in the constant company of Karl and Schuwald, continuing to act as the former's close confidante while currying favor with the latter. However, this proved to be part of Johan's grander ambitions to usurp Schuwald's business empire for himself, with the likely end of throwing the financial world into mayhem just as he had in other instances, such as his underground banking scheme, and, in this sense, his "friendship" with Karl may have just been a means to that ultimate end.
All the same, Karl is understandably hesitant to believe that Johan, for all of his heartless and duplicitous actions, was a wholly sinister being, as evidenced in Another Monster. While acknowledging the fact that Johan had adopted him as a better substitute for Edmund Fahren in attempting to manipulate his father and having previously held some perplexity at his motivations (eg. his apparent lack of fear at walking precariously on the edge of a rooftop), he seems to believe that Johan's display of sympathy to his plight was truly heartfelt. Likewise, Lotte Frank contends that she believes Johan had no intentions of killing Karl due to some apparent proclivity for the similarity of their situations.
Hans Georg Schuwald
Karl is the son of Helenka Nováková , a prostitute. When he was a young boy, she gave him some money and sent
him off on a train because she knew sending him away would give him a better life than staying with her. Shortly before boarding, he asks why his father, Hans Schuwald, won't help them, as he heard some ladies talking about him being Karl's father. She begins to weep, and tells him he can go see Schuwald when he's all grown up, but not to hate him if he turns him away, because "mommy doesn't hate him, even now.". He was left by his mother a train station, but before she left, she gave Karl the Rabbit's Foot given to her by Schuwald before they parted ways. He never saw his moter again after that. From there, he gets on the train and is thrown around between foster parents before settling with the Neumans.
- Main article: Another Monster
Werner Weber meets for an interview with Karl, who summarizes the events that took place for him. He says he and his father are doing well, and that Schuwald, even though he still works in business, isn't as vicious as he used to be. Karl also adds that he has decided to take on the last name of Schuwald. He said he still does not a full grasp of what has happen between Johan and and all the people he knows involved in the incident.