Gozu.

Gozu (牛頭) is an oni-like demon with the head of an ox and the body of a powerful infernal guard. In Japanese Buddhist imagination he is immense, muscular, and terrifying, a creature built less for cunning than for relentless force. The ox head makes him feel heavy, unstoppable, and judicial, as if brute animal power has been drafted into the bureaucracy of hell.

Gozu is among the first beings encountered on the road through the underworld. He guards entrances, escorts souls, and helps ensure that no condemned spirit slips away from its appointed punishment. In popular explanation, if someone somehow fled from hell, Gozu and his counterpart Mezu would be the ones sent to drag the soul back. He therefore interacts with the dead as a custodian of inevitability.

Gozu entered Japan through the larger Buddhist transmission of underworld cosmology from India through China. Japanese religion did not invent the idea of animal-headed infernal beings, but it adopted and localized them inside the courts of Enma and the vivid imagery of jigoku. In that setting, Gozu became one of the best-known wardens, a specific face for the machinery of postmortem punishment.