Herman Preminger is a primary antagonist in the series and is the current heir to the Preminger estate, a position he is desperate to secure for himself despite the wishes of his father, the Duke. He is the younger brother of Colette Preminger, a fact that highlights their starkly different natures, as he is depicted as sneaky, greedy, and driven entirely by self-interest. As the uncle of the protagonist Nadja, he is determined to get his hands on the family fortune no matter the cost and will stop at nothing to ensure he inherits the duchy.

Herman's primary motivation throughout the story is to inherit the Preminger fortune, and he views Nadja as a direct threat to his claim. His role in the narrative is that of the main villain, actively working to prevent Nadja from discovering her true heritage and claiming her place in the family. He is responsible for impeding Nadja's search for her mother and for manipulating events from behind the scenes. To achieve his goals, he co-opts the bumbling detectives Rosso and Bianco, who were originally working for his father, and hires them to find Nadja with the specific goal of stealing her brooch, which is the primary proof of her identity and lineage. When his initial plans prove insufficient, he encounters an unexpected ally named Rosemary, and together they devise a much more disturbing new plot: to have Rosemary impersonate Nadja and thus trick his father into accepting a false heir, thereby consolidating his own hold on the inheritance.

Herman's personality is characterized by cynicism and ill intentions, and he is generally disliked by other characters for his obvious scheming. His key relationships are defined by his greed and manipulation. He is in opposition to his father, Duke Preminger, who is resistant to Herman's ambitions. He is also in conflict with his sister Colette and his niece Nadja, whose existence he seeks to erase from the family line. He views Rosso and Bianco as mere tools to capture Nadja and recover her brooch, showing no loyalty to them. Later, he partners with Rosemary, using her deception to further his own agenda.

In terms of development, Herman’s schemes escalate as the story progresses. Initially focused on retrieving the brooch to destroy Nadja's proof of heritage, he later orchestrates a complex identity fraud to supplant her entirely. He is shown to be ruthless, even torturing a character known as the Black Rose to get information about Nadja and the brooch. His plans, however, ultimately unravel. In the final episodes, following a confrontation where Nadja escapes his clutches with help from Rosso and Bianco, his deceptions are exposed, and he is ultimately jailed for his crimes. While Herman does not possess any supernatural or special abilities, his notable skill lies in his manipulative nature, using his resources to hire others to do his dirty work and creating intricate schemes to deceive his own family.