Though well-associated with the plane of Baator, common minions of the baatezu at home and offplane, the history of the hell hound spreads well beyond that mere association. Even today, these hounds can also be found on Acheron, Gehenna, some areas of the Grey Waste, and as far as the planes of Fire or Magma.
Long before the baatezu near-adopted the entire species for their own, the hell hound was a native of the violent, fiery lands of Chamada on the plane of Gehenna, a smaller subspecies of the yeth hound. They were at the time still mere wild spirits, with no care for mortals but for a natural ire towards those that would act against the cycle of life, manipulating the souls of either themselves or others for their own desires. While some were taken and domesticated by Charon, for the most part they were left to their own whims.
Their natural strength, however, drew the attention of the baatezu during the first expeditions onto Gehenna, who captured a good number for domestication at Baator. A number of training camps were established; many of these still breed hell hounds today, including the great camps of Nessus. By the time of the War of Law and Chaos, hell hounds were well-established in the Baatorian forces, joining the fiends of Law on every front but especially noted for their contributions on the plane of Fire alongside the efreet of Imix, their viciousness easily driving the djinn from the Plain of Burnt Dreams. So successful were they that the efreet requested, and were granted, dozens of packs of their own; while they were naturally resistant to flames, these hounds were specially bred for the conditions of the Inner Planes, forming the seed for the hounds that dwell there even today.
In the wild, hell hounds tend to congregate in packs of between 10 and 40 strong, led by a single alpha; either male or female, merely whichever can hold control over the pack. Wild hell hound packs are heavily territorial, staking out a territory of up to 15 square miles as their own hunting grounds. They feed on their prey where they fall, wherever that happens to be, as their entire territory is all theirs; in the wild, hell hounds are most commonly at the tops of their food chains, and have little to fear from others in their lands. They are very adaptable hunters, and when exposed to a new environment and new prey, a hell hound pack will learn within weeks how best to tackle their new situation.
Domesticated hell hounds tend to be very attached to their master or masters, much as more traditional dogs. While they are more intelligent than mortal hounds, and certainly are able to distinguish their own kind from their masters, they still hold a natural respect for those able to show them better ways, and lead them properly in a hunt.
Hell hounds are pure carnivores, and usually peak predators at that, feeding on just about whatever they can hunt down within their lands whatever it happens to be. Though spiritual in nature, they do require food to survive; unlike most all living beings, though, they need no water to sustain themselves. Hell hounds have a natural sense towards the living that aids them in hunting, especially responding to those spiritually strained in one way or another: necromancers, the undead, those whose spirits have been relocated or damaged, and the like. Some breeds of hell hounds have been guided towards enhancing this ability, granting them an ability to sense the living even through the protection of illusion or invisibility, but this talent is far from common.
The lifespan of a hell hound is unknown, but given the infinite expanses of the planes, it's quite possible that they are in fact immortal. It is known that when a pack grows too large to be easily managed by its alpha, the pack divides, the next most dominant hound splitting off with a number of the pack's members to stake out new hunting grounds elsewhere. Hell hounds most often require extremely hot conditions to reproduce, environments of at least 1,000° F — usually in the midst of a flame or near to lava flows — but they have rarely been successfully bred in more mortal-friendly conditions. Hell hound pups reach full maturity by two months' time and full size no more than two months after that, but take well and quickly to training over that time.
Hell hounds largely resemble the larger breeds of mortal dogs, though well scaled up in size, with coats most commonly dark red, brown, grey, or black, and bright red eyes that catch light much as a cat's. At birth, wild hell hounds are only slightly larger than a canine pup, but once they reach their full size they stand from 2-½ to 3-½ feet at the shoulder, usually weighing anywhere from 20 to 60 pounds. Baatorian hell hounds tend to be much larger, reaching sizes from 4-½ to 5 feet tall and weights upwards of 150 pounds, and the well-known Nessian warhound can easily exceed 6 feet and 250 pounds.
- Monster Manual, pg.151
- Monstrous Manual, pg.187