|Behind the scenes|
Jakob was first introduced in The Golem's Eye. A playful boy, he invited Kitty to play cricket with him in a private magicians' park. While playing, their ball went over the park wall, into the magicians' part of the city and broke something glass. Jakob and Kitty quickly fled but were caught up by Julius Tallow and his djinni, Nemaides, who told them they had shattered his Rolls Royce's windscreen. The magician ordered his demon to unleash a Black Tumbler on the two. Both children survived, but Jakob was injured, while Kitty remained unharmed due to her magical resilience.
In the subsequent months, Jakob recovered from the attack, aside from black and grey marks across his face. He did not attend the court hearing against Julius Tallow. However, he did tell Kitty about a plan to doctor Julius Tallow's books the next time he sends them to his father's firm. This alteration succeeds in giving Julius Tallow's skin a yellow colour, and then eventually results in the magician's death.
During the Golem Affair, Nathaniel orders Bartimaeus to kidnap Jakob. He is then used as bait to lure Kitty out of hiding. Kitty takes the bait, but manages to escape with Jakob and the two are proclaimed dead by the authorities. They spend the next few days hiding in a hidden room in Jakob's father's factory, where Jakob's father and brothers forge new identities for them. Jakob then moves to the Council of Brugges, a commoners' city, to live with his cousins.
Originally, Jakob was slight and had an open, impudent face. He also had long, dark hair, down to his shoulders.
After being hit by the Black Tumbler, his face acquired an ashen colour, with smoky bands of black and grey. His hair was also shaven off during his recovery, but grew back soon afterwards.
Initially Jakob was a cheerful and energetic person. He also had an affinity towards his homeland, which was evident by his moroseness after discussions in school regarding the Czech. He also liked games, spending many hours playing in his garden.
After the Black Tumbler incident, he became increasingly introverted, refusing to go outside and working from his bedroom. However, he began to regain his confidence right after the Golem Affair, realising that not may people noticed his discoloured skin.
Mr. Hyrnek: A small slight man, with skin like leather. He is Jakob's father and a book-binder by profession. Jakob has the utmost respect for him saying that no one can rival his father in adorning book covers.
Mrs. Hyrnek: A large lady with broad shoulders, full of energy. She is Jakob's mother and dominates the household. She is also on good terms with Kitty's mother, who was her former colleague. When they both lost their jobs, Mrs. Hyrnek got Kitty's mother a job as a cleaner at a printing firm.
Grandmama Hyrnek: Claimed to be a 102 years old, Jakob's Grandmama was tiny, with little black eyes and a wrinkled face. She seemed to know a bit about demons, telling Jakob about their preferred forms and giving Kitty a silver pendant to protect herself with.
Karel, Robert and Alfred: Jakob's older brothers. All three of them had inherieted their mother's physique. They worked along with their father at the family's printing press.