Nezumi Otoko is a rodent-like half-human, half-yōkai hybrid over 300 years old. He presents a human-like appearance with prominent buck teeth and facial whiskers, typically donning a long brown cloak that conceals his ringworm and scab-covered skin. His notoriously poor hygiene, including a claim of never bathing, produces uniquely potent body odor and bad breath capable of incapacitating opponents at a distance. Flatulence functions as both a defensive mechanism and, in some depictions, an unconventional propulsion method. Sharp rodent teeth and iron-strong whiskers supplement his physical capabilities, alongside his tendency to deliver quick slaps that earned him the nickname "BiBiBi no Nezumi-Otoko". His origins remain ambiguous across official media. While often described as born to a human and a yōkai, other accounts depict his mysterious appearance as a human infant on a rat-inhabited island. Exploration of a "Nezumi-Otoko World" in the *GeGeGe no Kitarō: Kitarō Jigoku Arc* suggests "Nezumi-Otoko" is a species designation rather than a personal name, revealing his true name as Peke Peke. This arc introduces his mother, Mami, though her authenticity is later questioned. He references a biological sister, Nezumi-Onna, and a nephew, Nezumi-Neko, though these relationships are rarely explored. Ostracization from both humans and yōkai due to his half-breed status marked his early life, contributing to his later behaviors. His personality centers on greed, laziness, and self-preservation. Money and food are primary motivators, driving constant, often inept, schemes involving fraud, theft, or selling others to monsters. He frequently poses as a "Yōkai Professor," claiming dubious degrees in "Lazy Studies" or "Filth" from the "Bizarre University." Despite proclaiming himself Kitarō's "best friend," he readily betrays him or allies with stronger foes for flattery or monetary gain, displaying nonexistent pride when endangered. This treachery includes releasing sealed yōkai, poisoning attempts, and severing Kitarō's arm in one instance. However, genuine moments of loyalty surface, such as risking his life to save Kitarō from Wanyūdō or refusing to betray him under duress before succumbing to hypnosis. A deep-seated loneliness manifests in his vulnerability to familial deception, like being tricked by Shinigami posing as his brother. His relationship with Kitarō is complex and enduring. He addresses Kitarō casually and often exploits their association for profit, acting as his self-appointed agent or impersonator, leading Kitarō to force restitution. Despite betrayals, they share moments of camaraderie like casual drinks or joint vacations, and Kitarō consistently aids him in peril. Nezumi Otoko exhibits occasional genuine concern for Kitarō's safety, scolding those who harm him. Interactions with other yōkai are typically antagonistic, particularly with Neko-Musume, whom he fears and considers a natural enemy, expressing a dying wish to slap her. Hakusanbō is noted as a long-term acquaintance. Festivals or events often feature him as a commentator or vendor. Reactions to his apparent death vary—from harsh dismissal to genuine grief, especially from Neko-Musume—yet his presence is acknowledged as vital for atmosphere. Shigeru Mizuki, the creator, emphasized Nezumi Otoko's narrative role as a counterpoint to Kitarō's altruism, voicing themes of self-interest and social satire originally intended for the series. The character served as Mizuki's autobiographical mouthpiece in works like *Showa: A History of Japan*, reflecting his philosophies on survival and materialism. Mizuki based the character partly on his friend Umeda Etaro, known for failed get-rich-quick schemes.