Hellhound

Hellhound usually refers to someone who takes on a fierce, relentless, and powerful role, often embracing aggression, intensity, and a protective or fearsome demeanor.

Outside of kink, a hellhound is a supernatural dog with black fur, glowing eyes, and sometimes fiery breath. It's seen in myths around the world as a guardian (e.g., Cerberus), soul-reaper, or death omen.