Dogusaburō Oniyama leads the police department's anti-phantom thief bureau, obsessively dedicated to capturing the phantom thief Joker. Though his relentless pursuit defines their dynamic, his attempts invariably fail or backfire comically. Yet he displays genuine commitment to justice and underlying concern for Joker's safety, warning him of missiles or showing worry when the thief is poisoned.

Physically, Oniyama possesses a long, thin mustache, a prominent bald patch, a mole between his eyes, and sharp-looking teeth. He typically wears a parrot green suit, black tie, and black shoes. He has a wife and a daughter, Haruka Oniyama, whom he deeply cares for, experiencing significant distress when she is endangered. His family dynamic reveals he cannot defy his wife or daughter, often finding himself roped into shopping on his days off.

Oniyama's personality blends zealous hatred for Joker, viewing his capture as his life's purpose and pursuing him internationally, with hidden compassion, reluctantly cooperating during extreme crises. His fixation borders on addiction; he loses all energy and considers resignation when Joker is captured, instantly revitalized upon learning of the thief's escape. This complex relationship earned him Joker's respect for his strong morals and unwavering duty.

His personal details include blood type A, Scorpio star sign, favorite food fruit parfait, preferred drama *Bark at The Sun*, and favored singer Saburō Kitajima. His surname incorporates a pun on the Japanese word "oni," meaning ogre or demon.