Inspector Koichi Zenigata is a Japanese officer of the International Criminal Police Organization, better known as Interpol, who has dedicated his entire career to the pursuit of one man, the master thief Arsène Lupin III. Originally a member of the Tokyo Metropolitan Police, Zenigata became so consumed by his first encounter with Lupin that he left the Japanese force to join Interpol, granting him the international jurisdiction necessary to chase the thief across the globe. Standing at 181 centimeters tall with a sturdy build and a prominent chin, he almost always appears in a signature trench coat and fedora, a visual representation of his single-minded, unwavering mission.

On the surface, Zenigata often appears as a bumbling and overzealous officer, prone to dramatic outbursts, weeping openly, and being outsmarted by Lupin's elaborate schemes. This comedic exterior, however, conceals a remarkably skilled and competent detective. He is a master of judo and karate, an expert marksman with a Colt M1911 pistol, and possesses a nearly superhuman level of endurance and determination. His most distinctive technique is the use of his handcuffs as a projectile, throwing them in a bola-like arc to ensnare criminals from a distance. Zenigata's stubborn refusal to give up, combined with his sharp intuition, allows him to consistently track Lupin to his location and see through his disguises, even if he is ultimately unable to secure a lasting arrest.

Zenigata's personality is defined by a deep, complex, and often contradictory obsession. His stated goal is to capture Lupin and bring him to justice, yet his actions reveal a man who is fundamentally sustained by the chase itself. On several occasions when he has successfully captured Lupin, he becomes frustrated and almost depressed when the thief does not immediately escape, as a world without Lupin to pursue has no meaning for him. This attachment runs so deep that on the rare occasions Zenigata believes Lupin to be dead, he is utterly devastated, once even retiring from the police force to become a monk, having lost his sole purpose in life. While driven by duty, he also considers himself the only person with the right to take Lupin in, fiercely protecting his quarry from other criminals or law enforcement officers who might kill him. Despite his eternal frustration, a profound, unspoken respect and even friendship exists between him and Lupin. They are reluctant allies who will set aside their rivalry to face a greater threat, and each has gone to great lengths to avenge or rescue the other when their life is in danger.

Within the larger narrative, Zenigata serves as the primary antagonist and the ultimate foil to Lupin. While he is officially after all members of Lupin's gang, his focus is almost exclusively on the master thief himself, often ignoring his associates, Jigen, Goemon, and Fujiko, to pursue his primary target. This all-consuming obsession has come at a great personal cost. His life is one of perpetual pursuit, leaving no room for a family or a romantic relationship, and he is often portrayed as a lonely figure who laments his lack of personal connections, though he is unable to change his ways. Over the course of the long-running series, Zenigata has undergone significant development. Early depictions presented him as a more corrupt and ruthless officer, but he evolved into a more sympathetic and endearingly awkward character whose emotional vulnerability and hidden competence make him beloved. His humorous nickname for Lupin, Pops, is a staple of their dynamic, and his emotional breakdowns—often involving tears of frustration, joy, or relief—have become a defining character trait, showcasing a surprisingly sensitive nature beneath the gruff exterior of a man who has made chasing the world's greatest thief his life's work.