The Thoul is one of the most infamous goblinoid monsters to come out of Dungeons & Dragons, at least amongst the more venerable crowd of D&D players. These bizarre humanoids are a weird mixture of hobgoblin, troll and ghoul, and go all the way back to the original White Box supplement: Volume 3: The Underworld & Wilderness Adventures. Here, they appeared on the level 2 Monster Level Table - but only on later printings; the earliest printings had that slot filled by the Toad (Giant) entry, which supports the popular theory that thouls were originally a typing mistake that got past the editors.
But, Gary Gygax wasn't one to waste an opportunity; when people kept asking him what a "thoul" was, he explained it as a troll/ghoul/hobgoblin mix, giving it a similar name etymology as the more well-known gnoll (which, back then, was a gnome/troll). Why he added hobgoblin to the racial mix, nobody knows, but thouls were thus officially a thing, receiving their first official stat-up in Monster & Treasure Assortment – Set Three. Here, they were presented as having 2/1 Attacks, an Attack Level of 9, an Armor Class of 9, saving throws as a 3rd level Fighter, and the special ability to paralyze by touch. Thouls subsequently made it into the 2nd edition of Basic D&D, where their abilities were tweaked (Attacks were specified as 2 claw attacks or 1 weapon attack, and they received the troll-like ability to regenerate 1 hitpoint per round). From there, they languished in obscurity until they were converted to Advanced Dungeons & Dragons in the Mystara Monstrous Compendium Appendix. It was in this source that they first got any real description, although still pretty bare-bones - which probably contributed to their falling under the radar.
Thouls never made it into 3rd edition, except through the power of 3rd party publishing; Dave Arneson's Blackmoor, a D20 adaptation of the old-school D&D setting published by Zeitgeist Games, brought Thouls back due to their connection to Blackmoor and Mystara. Ironically, thouls would then return in 4th edition D&D; the article "Ye Olde Creature Catalogue" in issue #418 of Dragon Magazine would see thouls return as one of the creations of the ancient hobgoblin empire of the Nentir Vale setting.
The Mystaran Thoul, as mentioned above, was never particularly well-fleshed out. Their entire identity is wrapped up in their being a slave race to hobgoblins; although we know they were magically breed from crossing hobgoblin with ghoul and troll, we don't know who did it, how, or why. Their entry in the Mystaran MCA states that "Most thouls look just like hobgoblins: about 6½’ tall, dark skinned, and untidy. Some, however, show clear signs of their troll ancestry. Such thouls can have any of the following characteristics: relatively hairless skin with a greenish cast instead of the dark-red or reddish-orange skin of hobgoblins; slate gray or dull black hair, ropy in texture; long and tubelike noses like a troll’s, very different from a hobgoblin’s rather canine muzzle." Which raises a question of if the writer had ever seen the artwork for hobgoblins in AD&D. Like hobgoblins, they favor brightly colored clothing, usually favoring blood-red cloth and gleaming-black leather. Their weapons are always well cared for and brilliantly polished.
Socially, Mystaran Thouls either live as small isolated hunter-gatherer family groups, or are kept as slaves by hobgoblins and orcs. Hobgoblin leaders particularly enjoy using thouls as their bodyguards, but hobgoblins are stated as hating their crossbreed kin: those wretches unfortunate enough to live amongst hobgoblins without a powerful sponsor are outcasts, and often heavily abused. Which is really a rather stupid thing to do seeing as how thouls have razor sharp claws, paralyze on touch exactly like ghouls, and regenerate just like trolls. Making this even stupider, Mystaran thouls actually have the ability to become spellcasters, achieving either 5th level as Shamans (Necromancy, Healing & Charm spheres) or 4th level as Witch-Doctors (Illusion/Phantasm, Enchantment/Charm and Necromancy schools), which is one of the reasons why they're so valuable to other tribes of humanoids in the first place.
Thouls are cunning combatants who typically carry a sword and a bow. Though they relish the feeling of ripping flesh with their claws, which allows them to utilize their paralytic touch, they are well aware of the fact that those pesky elves are immune, which is why they always carry backup weaponry.
Thouls are a viable race, and living beings despite their ghoulish taint, but they have the lowest birthrate amongst humanoids. They live an average of 50 years.
The Nerathi Thouls are, ironically, probably more detailed than their Mystaran kin. These thouls were created by the ancient hobgoblin empire, which sought to create a super-soldier by using dark magics to fuse hobgoblins with trolls and ghouls. They succeeded in creating their monstrous offspring, but the results were... unsatisfactory. Although they had inherited the hobgoblinish brutality and militaristic outlook, especially due to their upbringing, they had completely failed to inherit the desired hobgoblinish traits of intelligence, tactical acumen and discipline. They were tough and strong, but savage and dimwitted, at least compared to what their creators had envisioned. The project was abandoned and the thouls were left to make their own uneasy way into the world.
Nerathi thouls clearly take after their hobgoblin ancestors, although their green skin, long nose and coarse black hair all make their trollish ancestry plain to see. Their ghoulish taint manifests mostly in the length of their black, claw-like nails, their sharp teeth, and their long tongues. Courtesy of their distant giant ancestry by way of their troll progenitors, thouls are invariably tall and muscular, especially compared to the hobgoblins around them. For cultural reasons, thouls favor the bold crimson and black colors worn by their hobgoblin kin, and they take exceptional care of their gleaming black leather armor, a practice drilled into them by their cruel hobgoblin taskmasters. Like their Mystaran kin, Nerathi thouls are living creatures, and their tainted blood has a marked negative impact on their fertility - in fact, forced breeding programs were instrumental in producing the race, and even today, some ambitious warlords still use it to swell the ranks of their armies with these mutant goblinoids.
Unlike Mystaran thouls, Nerathi thouls have four distinctive cultures, based on whether they have tried to integrate into goblinoid society, orc society, or ghoul society, or just chosen to go it alone.
Individualist thouls pursue simple lives, gathering in family groups and doing whatever they have to in order to survive, which most often requires turning to banditry or mercenary work. These thoul tribes are often sought out by would-be warlords of many species, given their lethal prowess and sheer durability. More savage species, such as orcs, often raid these tribes in an attempt to carry off young thouls to rear them as slaves, which certainly doesn't predispose the thouls to like other races much.
Thouls that have chosen to live amongst their fellow goblinoids fall into two subcultures. Those fortunate enough to live amongst normal goblins and/or bugbears benefit greatly from their physical abilities and quickly rise to the top under that age old tradition of being able to shrug off assassination attempts and strong enough to kill & eat anyone that annoys them too much. Those thouls that live amongst hobgoblins, however, are not so fortunate. Hobgoblins hate thouls for their "mongrel blood" and fear them for their superior physical abilities. As such, they treat thouls as second-class citizens at best; those thouls who lack a hobgoblin sponsor typically rely on their regenerative abilities to survive the abuse heaped on them by their kin, and are blatant outcasts to anyone's eyes. Sponsored thouls typically serve as elite bodyguards, gladiators, or vanguard shock troops; in fact, many hobgoblins breed thouls specifically for these purposes, and scar them with acid and fire while young to constantly remind them that they are little more than slaves. Hobgoblin commanders spare little thought for their thoul troops, and regularly dispatch them on suicide missions. Consequently, thoul soldiers hate their masters, but conditioning keeps most in line. Those who rebel find one of two ends — escape into the wilds or death at the stake for insurrection. Thouls who dwell amongst hobgoblins ardently worship Bane and believe that he created them as his chosen people. They are so dedicated to the Lord of Darkness that they even refuse to honor his exarchs, and they hold Maglubiyet in particular scorn. As a sign of their faith, thouls prominently display Bane’s holy symbol on their clothing and armor and strive to live up to his harsh precepts and gain his blessing. They also believe that the many hardships the thoul race experiences at the hands of their hobgoblin masters are a divine test that they must endure. The hobgoblins, unsurprisingly, foster and manipulate this religious belief.
Ironically, thouls actually have it better amongst orcs than they do amongst their own hobgoblin kin! Whilst it's true that orcs also value thouls as bodyguards and elite warriors, the more rough & tumble, chaotic society of the orc places less importance on ancestry, so thouls can go very far indeed on their physical prowess. Indeed, orcs treat thouls as being as close to equals as they are capable of treating anybody, and thouls thrive in orc society, often rising to command raiding parties and warbands of other "mongrel" orcoids such as Half-Orcs, troll-orcs, and ogrillons. Being treated so well engenders a fierce loyalty amongst thouls, and these thouls shun the worship of Bane to instead worship Gruumsh, particularly favoring his Exarches Bahgtru and Vaprak.
The final form of thoul society is that which strives to embrace its ghoul ancestry and become undead themselves, seeking the power and immortality they perceive ghouls as possessing. Often worshipping Orcus and/or Doresain, these thouls seek out and infest areas that are traditionally home to ghouls, such as cemeteries, necropoli and catacombs. Such thouls attempt to make themselves look more ghoulish by wearing tattered clothing, coating themselves with grime, and shunning weapons. A few of these thouls succeed in establishing a collaboration with actual ghouls. Ghouls, cunning by nature, appreciate the benefits of allying with a more powerful creature, especially one able to protect them from troublesome clerics and paladins. Such an alliance, however, does not prevent a ghoul from ruthlessly exploiting its dimwitted ally; for example, some ghouls demand a daily tribute of a thoul’s flesh in exchange for letting it join a ghoul pack or as a form of down payment on a future unholy rebirth. Occasionally, a thoul bent on achieving undeath works as an underling for a necromancer, a vampire, or a lich, in the hope that its master will help it achieve its transformation.