They often have to guard the entrances to the world of the dead, such as graveyards and burial grounds, or do other things related to the afterlife or the supernatural. These might be hunting down lost souls or guarding a supernatural treasure. In European legends, seeing a hellhound or hearing it howl may be either an omen or a cause of a soon death.
It is said to be bigger than a normal dog. Hellhounds are often said to have black fur, glowing red or sometimes glowing yellow eyes, a lot of strength or speed, ghostly or phantom features, a bad smell, and sometimes even being able to talk. In cultures that think that there is fire in the afterlife, hellhounds may have fire-based abilities and looks.