Koichi Zenigata, known widely as Inspector Zenigata, is a central figure in the Lupin the 3rd series. Originally an inspector for the Tokyo Metropolitan Police Department, his pursuit of the thief Fujiko Mine led him to New York, where he met Arsène Lupin III for the first time. This encounter fundamentally altered the course of his life. Obsessed with capturing the master thief, he left the Japanese police force and enlisted in the International Criminal Police Organization, or Interpol, to dedicate himself entirely to Lupin's arrest. He is a descendant of the legendary fictional detective Heiji Zenigata.

Zenigata is defined by his single-minded obsession with capturing Lupin. This drive is so absolute that it consumes his personal life, leaving him without a family or a home. While his tenacity makes him appear as a tireless and competent pursuer, he is often portrayed as bumbling and gullible, frequently falling for Lupin's tricks. Despite this, he is a master detective capable of correctly predicting Lupin's moves, even if he cannot thwart them. He is incredibly emotional, often weeping openly when Lupin escapes, shows him a surprising kindness, or is feared dead. Above all, he believes that he, and only he, has the right to capture Lupin. This possessive form of respect forms the bedrock of their complex relationship. His overall character evolved from a cynical and violent officer in the earliest stories to a more endearing, awkward, and warm-hearted individual, though his core determination remained unchanged.

Zenigata serves as the direct foil and primary antagonist to Lupin III, creating a dynamic conceived as a human version of Tom and Jerry. He relentlessly chases Lupin across the globe, acting as the primary representative of the law in a world of thieves. The relationship between Zenigata and Lupin transcends simple enmity. They are, in a way, friends. Lupin greets him with mock affection, and Zenigata, despite his protests, shares a deep, unspoken bond with his quarry. They have worked together on numerous occasions to face greater threats, demonstrating that their rivalry is built on a foundation of mutual respect. When Zenigata is injured or believed dead, Lupin will avenge him. Lupin's partners, Daisuke Jigen, Goemon Ishikawa, and Fujiko Mine, are also targets of Zenigata's pursuit, but they generally take a back seat to his primary obsession with Lupin. Fujiko Mine is known to manipulate Zenigata for her own ends.

Throughout the series, Zenigata displays considerable growth, most notably in the mellowing of his personality. His absolute commitment to his mission has led him to take extreme measures, such as becoming a monk after believing Lupin had died. Despite his frequent failures, he remains a highly respected officer within Interpol, largely because his obsessive hunt for Lupin results in the capture of countless other criminals as collateral. His abilities are formidable. He is an expert detective and tracker with a relentless will. He possesses superhuman endurance and resilience, able to shrug off injuries and recover with startling speed. His signature method of arrest involves a set of handcuffs attached to a long rope, which he throws expertly to capture fleeing suspects, a technique inherited from his ancestor. He is also proficient in martial arts and, when necessary, will use a sidearm. His tenacity and investigative skill make him a uniquely persistent adversary who is never far behind.