Detective Kogoro Mouri is a private investigator and the father of Ran Mouri. He attended Teitan High School alongside his future wife, Eri Kisaki, and later graduated from Beika University, where he was the ace of the judo team. Prior to his career as a private eye, Kogoro served as a police officer in the Tokyo Metropolitan Police Department’s First Division, working under Inspector Megure. His departure from the police force, as well as his subsequent separation from his wife, is linked to events depicted in the second film.

Outwardly, Kogoro presents the image of a lazy and unprofessional detective who would rather laze around than work. He is easily infatuated with beautiful women and is a devoted fan of the pop idol Yoko Okino, keeping a collection of her merchandise and never missing her television shows. He frequently drinks alcohol, often leaving empty beer cans around his office, and is a heavy smoker. This behavior often embarrasses his daughter, Ran, and is cited as a primary reason why his estranged wife, Eri, chooses not to return home. Despite his constant feigned disinterest, Kogoro still harbors deep feelings for Eri and has asked her to move back in. His genuine care surfaces most prominently when his family or close friends are in danger, at which point his entire demeanor shifts to a serious, focused, and surprisingly capable investigator.

Throughout the series, Kogoro's reputation as a great detective is largely undeserved, as he typically misses obvious clues and jumps to hasty conclusions. This ineptitude led to his nickname, Sleeping Kogoro, which originated from his habit of solving complex cases while appearing to be asleep. In reality, these deductions were being fed through him by Conan Edogawa, who knocks Kogoro unconscious with a tranquilizer dart and uses a voice changer to impersonate him. Kogoro himself is unaware of this arrangement and genuinely believes the acclaimed deductions are his own brilliant thoughts coming to the surface when his brain works at full power. Nevertheless, when a case involves someone he personally cares about, his intuition sharpens, allowing him to connect dots and solve crimes without Conan's intervention, demonstrating an understanding of interpersonal relationships that often exceeds that of the young genius.

Physically, Kogoro is far from helpless. In his college years, he was an expert in judo, and he remains a capable fighter. He is also an excellent marksman with impressive accuracy. He possesses a notable fear of heights in the film adaptations. Though his professional detective skills are generally poor to average, he follows police procedures and asks the right questions, suggesting a foundational competence when he applies himself.