TV-Series
Description
The Doktor is an antagonist in the anime Yu-Gi-Oh! Arc-V. He serves as a high-ranking member of Duel Academy, identified by the character Sora Perse as one of the inner circle of the Professor, Leo Akaba, the leader of the Fusion Dimension forces.

Physically, the Doktor is a tall and thin elderly man with a gaunt and unsettling appearance. He has sunken eyes and cheeks, bags under his eyes, small green pupils, and long white hair that is styled in a manner reminiscent of another character from the franchise, Rex Goodwin. His attire consists of a long dark grey coat with an orange-brown center section patterned with yellow lines, worn over grey pants and black shoes.

In terms of personality, the Doktor is portrayed as ruthless, sadistic, and highly manipulative. He takes great pleasure in using his creations to control others and displays a confident, almost arrogant, pride in his work. He is driven by a scientific curiosity to perfect his methods, constantly seeking to improve his parasitic monsters whenever a flaw is exposed or an unexpected outcome occurs.

The Doktor's primary role in the story is as the creator of a series of Parasite Monsters, most notably the card Parasite Fusioner. His most significant ability is the power to brainwash individuals by implanting these parasitic creatures into their bodies. According to Sora, this process grants the Doktor the power to alter a person's heart and mind, forcing them to act according to his will. Before his direct involvement in the main plot, he is revealed to have already used this ability on several key characters, including Rin, Lulu Obsidian, and Celina. He later also implants a parasite in Zuzu Boyle.

Within the narrative, the Doktor operates from the shadows of Duel Academy, often watching events unfold on monitors alongside the Professor. He takes a personal interest in the mental subjugation of the four braceleted girls, viewing them as successful experiments. He is directly responsible for forcing Rin, Lulu, and Celina to Duel against their loved ones, observing the results with clinical glee. When the protagonists begin to resist his control, such as when Yuya Sakaki is able to expel a parasite, the Doktor becomes intensely curious, viewing Yuya as a new subject for his research.

The Doktor's key relationships are primarily defined by his professional allegiance to Leo Akaba, whom he addresses as a fellow researcher. While loyal, his obsessive curiosity ultimately overrides his caution. His most notable relationship is with his victims, whom he sees not as people but as hosts for his experiments and a source of valuable data.

The character's development culminates in his demise, which is a direct result of his own nature. After successfully capturing the four girls, the Doktor requests that the Professor leave Yuya to him so he can experiment further. When Leo hesitates, the Doktor expresses overconfidence in his parasite work and argues that as fellow researchers, they should share a curiosity for challenging research. However, the Professor disagrees, citing that his own past curiosity was what led to the creation of the world-ending Supreme King Dragon Zarc. As a result, Leo uses his technology to seal the Doktor into a card, permanently removing him from the story and freeing the brainwashed girls.

Regarding notable abilities, aside from his mind-control parasites, the specifics of the Doktor's own Deck are never fully revealed. Only his key spell card, Parasite Fusioner, is shown. However, he refers to the Deck used by a brainwashed Celina as his Parasite Deck, suggesting that his strategies revolve around Fusion Summoning to bring out powerful parasitic monsters like the Parasite Queen.