Alucard serves as the unwaveringly loyal butler to the young detective Mamiya Mugen. He presents as a large, bald old man possessing significant physical strength, often underestimated due to his unassuming appearance. His origins trace back to Transylvania, carrying vampiric heritage, though his precise nature—whether vampire, dhampir, or another entity—remains deliberately ambiguous, signaled by his name directly inverting "Dracula." His absolute devotion to the Mamiya family stems from Kyoshiro Mugen saving his life during World War I, cementing his lifelong role as Mamiya's protector and aide.

In the OVA adaptation, Alucard demonstrates abilities beyond human limits. He can transform into a more monstrous state when necessary, revealing enhanced strength to combat threats like crocodile-headed henchmen during rescues. Despite this capacity for violence, he typically maintains a gentle and composed demeanor, reserving his supernatural power for critical situations. His duties involve both practical assistance in investigations and physical protection, often working alongside Mamiya and Inspector Edogawa to confront criminals. Alucard's relationship with Mamiya blends paternal guardianship with professional duty, frequently advising and supporting the detective during cases involving occult or criminal elements.

His background includes service across multiple iterations of the manga's continuity. In the second and most prominent continuity, he aids Mamiya and Atsuko Fukune against adversaries like Dr. Lao and Kaitō Kurenai Okoze, reflecting his adaptability to both comedic and darker narrative tones. While lacking extensive personal development arcs, his consistent presence acts as a stabilizing force for Mamiya. The character's design and traits position him as a likely influence on later "Alucard" tropes in anime and manga, though his story remains confined to the established plotlines of the franchise.