A hellhound is a supernatural dog, found in folklore. A wide variety of impish supernatural dogs occur in mythologies around the world. Features that have been attributed to hellhounds include black fur, glowing red or sometimes glowing yellow eyes, super strength or speed, ghostly or phantom characteristics, foul odor, and sometimes even the ability to talk.

Legend says that if someone is to stare into its eyes three times or more, the person will definitely die. In cultures that associate the afterlife with fire, hellhounds may have fire-based abilities and appearance. They are often assigned to guard the entrances to the world of the dead, such as graveyards and burial grounds, or undertake other duties related to the afterlife or the supernatural, such as hunting lost souls or guarding a supernatural treasure. In European legends, seeing a hellhound or hearing it howl may be either an omen of death or even a cause of death.