Tartarus is a subdimension that hangs off of the underside of Equestria like a hyperdimensional barnacle. It is far easier to enter than to leave. This is by design. Open lava flows, subterranean caverns of angry red stone, the wails of the imprisoned, all are essential aspects of Tartaran ambience. This is not by design. Tartarus was originally a featureless void, but the thoughts and power of those trapped within have warped it into a place as dark and hostile as they.

And yet, there is life. Bizarre, alien, often cruel and sadistic life, but life. The same energies that reshaped Tartarus are still present, but the subplane can hold only so much anger, resentment, and shame at once. Once past the point of supersaturation, some condenses into a self-aware knot of negative emotions, free to scuttle about the blasted landscape.

The changelings call these beings the Unloving, the griffins, dvergar. The horses of Saddle Arabia call them shaitani, the camels, qlippoth. Rams know them as grogim, deer as rog. Diamond Dogs refer to them as the Deep Ones (which are entirely different from what a seapony would call a Deep One) and donkeys characteristically cut to the heart of the matter and term them Tirek's get. For the sake of convenience, this discussion will use the pony term, "demon."

Tirek and the Magnus

The story of Tartarus's creation goes back to the earliest days of Equestria, when Faust walked the earth and the world was still being made and populated. Equestria is, first and foremost, a world of balance, for good and for ill. Indeed, of good and ill. The good intentions, hopes, and dreams of the twin creators cast a deep, dark shadow of malice and cruelty. This was Tirek, the First Demon.

As the living antithesis of the creators' will, Tirek's sole purpose was to destroy everything they made. Both opposed him, but he was just as powerful as they, and far better suited for combat. After a few skirmishes that were stalemates at best and ruinous at worst, Faust and Discord decided that, to put it bluntly, fighting was for chumps. So they made a better chump, the only creature of her kind ever seen in Equestria before or since: the Magnus, Champion of Law and Chaos.

Just as Tirek was made to destroy creation, so was the Magnus made to destroy him. The battle was a terrible thing, too great for history to forget, but too horrible for it to remember the details. For three days and three nights they fought one another, until finally, bereft of an arm and most of her blood, the Magnus stood triumphant.

Of course, there was the matter of what to do with the body. Without a conscious will holding it together, Tirek's corpse would disperse, and the constituent energies could then reform into an even more dangerous monster. The twin creators knew this, and used the time given to them by the epic battle to prepare the next stage of their plan.

The moment Tirek's form struck the ground, it was whisked away to the very edge of existence. Moments later, the sudden release of the volatile energies within caused a bulge in space-time, which was carefully turned ninety degrees from reality and tied off like a balloon. Thus, Tartarus was made. The newly created pocket dimension proved to be incredibly useful as a place to store those too dangerous to destroy. Cerberus, originally created as a steed and companion to the Magnus, was assigned as an ever-vigilant guardian, one of the greatest lines of defense against anything that might escape the pit, though far from the only one.

As for the Magnus herself, after the final battle, she travelled the world, putting right what Tirek had made wrong. The creators were too busy finishing the work of creation, and the timetable was too precarious for them to spend any time doing repairs on what was already complete. (Precisely why they had a timetable is best left uncontemplated by those who cannot work worlds into existence.)

By the time the last of Tirek's fell handiwork was scourged from the land, ponies had been created, Faust had gone dormant, and Discord had begun his slow, grieving spiral into insanity. Still, he was lucid enough to send the Magnus into a state of hibernation at the side of her loyal companion. She still stands vigil at the gates of Tartarus, touched by only one second every millennium. Should any of the prisoners cross the gates' threshold, the time spell will transfer from the Magnus to those fugitives.

While Tirek and the Magnus were major mythic figures in the pre-Discordian era, little survives from that time. Among ponies, they are but a pair of curiosities among the fragments of history before the Age of Chaos. They may have existed, they may have been legends, or they may have been products of the draconequus's fevered imagination, sown among the authentic artifacts just to make historians' lives that much harder.

Major Demons and Prisoners

The following are especially notable denizens of Tartarus, whether through power, influence, or some combination thereof.

Tirek
The First Demon, the Imprisoned Jailer, the All-Despising Pit

Tirek lives. A being such as he cannot be truly slain. In the near-perfect nothingness on the very edge of the universe, his awesome power expanded and reshaped itself, becoming Tartarus itself. The stone is his flesh, the lava is his blood. The prison is its greatest prisoner.

It is also its greatest jailer. Tirek's all-consuming hatred does not discriminate, and so he focuses it on whatever is nearest. Aware of every being within him, he lives to make them suffer, convulsing the substance of the subplane to wreak havoc with all within.

Still, while Tirek is omnimalevolent, he is not omniscient. He may be aware of presences within him, but he must focus on an area to sense it as a mortal creature does, or to reshape it. There are magics that can ward an area from the First Demon's active awareness, and demon cities are built in regions thus protected. The wards must be renewed with some regularity, and at times Tirek is calm enough to deduce the location of a warded area from the hole in his awareness, but the infernopoli offer safety and stability that far exceeds that of the wilds of Tartarus.

When Tirek has no other outlet for his rage, when he cannot feel the skittering feet of countless horrors on his reshaped flesh, then he lashes out at himself, causing great eruptions and hellquakes that devastate the entire realm. This upheaval lasts until he either finds something else to torment or exhausts himself, entering a torpor that can last for as long as a century.

Tirek's essence is still the primary source of Tartaran power, and to this day, demons tend towards horns and red-and-black color schemes. Ponies with these palettes are seen as inauspicious in more superstitious communities, but are no more demonic than any other.

Maxwell
To Whom Flame Bows, Coldest Logic, Master of Telekinesis

Maxwell is one of the most curious demons, in every sense of the word. He is a seven-foot tall humanoid apparently formed of jagged but regular obsidian crystals and surrounded by a thin layer of distorted air. His morphology lies somewhere between "robot" and "adolescent dragon." His only facial feature is a faint red glow in the center of his head.

In reality, he is composed entirely of ice, the distortion caused by continually deflecting the infernal heat of Tartarus from his body. This is a relatively minor example of his mastery over mentally directed force. He is unmatched in both strength and precision, able to part channels in the calderas of Tartarus, solidify them, and walk across them with ease. (Of course, he only does this during Tirek's periods of inactivity, lest the First Demon express his displeasure at being so manipulated.)

Maxwell is as emotionless as is possible for a demon. Where Grogar's heart is dead, his never existed in the first place. He does not feel hatred; he weighs relative utility and destroys those who are more useful to him dead than alive. He does not feel pride; he knows he is the best telekineticist in Hell because there is ample supporting evidence and none to the contrary. He does not feel fear; he acknowledges Tirek's superior power and acts in ways that perpetuate his own existence, as his self-utility would be zero if he were destroyed.

Though he may lack emotion, Maxwell does not want for ambition. Imprisonment limits him, and so he seeks to overcome those limits. He is certain that Tartarus could be easily escaped were it not for the subplane's continual convulsions. Therefore, Tirek must be subdued. The question of "how" has proven elusive.

Maxwell is most notable for his patronage of King Sombra. He taught the unicorn the dark magics that enslaved the Crystal Empire and the distortion that sealed it for a millennium. Sadly, prolonged contact with a mind so alien drove Sombra utterly insane, and what was to be Maxwell's new seat of power was instead ushered into a totally unrelated void.

Laplace
The Algorithm of Fate, the Actor and Stage, Puppet of Predestination

Laplace is an unusually pitiable fellow for a denizen of Hell. His power is what countless arcanists have coveted since the beginning of conscious thought: omniscience. And it is far more of a curse than a blessing.

Laplace's knowledge knows no limits. From the trajectory of every particle in existence to the secret true names of every living being to the sound of one hand clapping, nothing is secret to him. However, this includes the events of the future, and thence originates the title "Puppet of Predestination." Laplace knows his own fate front to back, and has no choice but to obey it. To do otherwise would be to invalidate his own knowledge, betray his nature, and destroy himself. Whether he would simply cease to exist or transform into a demon of ultimate falsehood, only he can say.

Knowing all the secrets of shapeshifting, Laplace appears however his fate dictates he should, whether that be a cloud of steam, a wizened unicorn, or even the form of Tirek before his defeat. His voice is always weary and disinterested, like a terminally bored actor. He surrendered any hope of escape from his causal prison long ago.

Dealing with Laplace is odd. He already knows how the entire exchange will go, and often sighs or otherwise indicates boredom when in a form capable of doing so. Even these seemingly involuntary tics are just more tasks he has been preordained to carry out. He never tries to rush the process, for he knows exactly how long it will take. At the end of the proceedings, he grants the agreed-upon boon, smites the presumptuous demonologist, or simply returns to Tartarus without doing anything else, as per fate.

He is usually invoked to answer three questions, and while he must answer them truthfully, as per his nature, there is no force binding him to answer them completely. Many have thought themselves clever to first ask, "What will happen after you answer my third question?" His answer is always the same: "I will take my leave." When presented with questions such as "Is the answer to this question 'no'?", he will explain why the question cannot be answered.

At first, it would seem that Laplace's mere existence denies the possibility of free will. This is not so. Similar to Tirek, he may know everything, but he is not consciously aware of all of it. So long as a datum is not under his direct scrutiny, it is free to bob in the winds of magic, chance, and choice. But once Laplace bothers to look, his gaze pins the fact, locking it into a state of absolute certainty. This is, in part, why he answers so vaguely; being the voice of destiny is a heavy burden, and it pleases him not to see a world moving in lockstep with his every pronouncement. (Little if anything pleases him, actually, but dictating the fate of the world especially.) He spends much of his time in meditation, intentionally emptying his mind to keep his impact on the future to a minimum.

Nothing can keep knowledge from Laplace's mind, but certain potent beings can obscure that information from his awareness. Most notable are how to bypass the gates of Tartarus and how to reconstitute Tirek from the Inferno, made inaccessible by a mental block placed by Discord himself during the Chaotic Era, lest the demons spoil his fun. The details of Laplace's own death are also kept from him, by his own fear. However, he is all too aware of when his time will come.

Grogar
Father of Necromancy, Lord of Tambelon, Soul-Hater
Perhaps the most notable of Tartarus's non-demonic residents, Grogar is forever remembered as the ram who codified and formalized necromancy, his notoriety preserved even through the Discordian Era. Many have compared him to Star Swirl the Bearded. The Bearded One himself considered himself greatly less than the Lord of Tambelon and was glad of it.

Grogar estranged himself from his kin at a young age, traveling the world and observing the many ceremonies each thinking race had developed for their dead. From the funerals of the ponies to the sky burials of the griffins, from the nautical pyres of the reindeer to the mummification of the camels, he bore witness to them all. And in all, he found the common element, the reason behind his quest: the soul.

Grogar despised the concept of the soul. It mocked him as something that could not be seen nor felt nor magically sensed, yet was clearly present. It was a question that even his formidable intellect could not answer. Every culture he visited had no answers for him, no explanation for this inscrutable vital spark.

You know what they say: it's always in the last place you look.

In the expanses of the Marengeti, Grogar finally found his answer, though it was far from the one he'd been looking for. The local zebra tribe's tradition of cremation was hardly novel at that point. What was was the reason behind it. They burnt their dead not to free the soul from an earthly cage or return it to the heavens as smoke. They burnt them as a show of respect, a promise not to use the corpse even after it was vacated.

Other species did not receive this consideration. Certain herbs, seeds, and clays, bound together with alchemy and zebra magic, made a reagent that brought motion and motivation to a dead body. These zombi were dull things, with no will of their own, but they were tireless as death itself and repulsive to predators. And, most importantly to Grogar, they had no souls.

From this foundation, the ram began his studies. At first, it was theoretical, translating the magics of one species to another. Then he left the tribe, grateful, and he began experimentation. One by one, he discarded the reagents as he refined his techniques, until all that he needed to raise the dead were black onyx and his own power. With no need for the exotic components of the zebras, he returned to his home in the Belon Ridge to continue his research. Many promising spells branched off of the basic ritual, offering numerous ways to blight the living and bolster the dead. Fear, decay, necrotic might, such were Grogar's watchwords.

In time, though, he hit a ceiling. Even a genius such as the Soul-Hater was only one ram, one who had reached the limits of his ingenuity. Worse, Grogar was growing old, and he had no way of raising his own corpse. There was no time to train an apprentice, and even if he did, once brought back to life, he would be subservient to the kid.

So, with mortals not an option, Grogar turned to the immortal. Demonology was almost laughably simple for him, the hateful wrath of Tirek merely a well-heated version of the cold hunger of oblivion. He summoned Laplace and, with courtesy that would astonish any but the Algorithm of Fate, asked how he might further his studies.

At Laplace's instruction, he then summoned Maxwell, to Whom Flame Bows. From naught but air, the demon granted Grogar three boons: a body that would not die until killed, a tome that would guide him whenever he could go no further in his studies, and a fortress where those studies need never be interrupted. This came at the cost of Grogar's own soul, which he surrendered gladly. The fortress he called Tambelon, the book, the Black Codex.

Grogar's work continued for centuries, for he was nothing if not careful. Inspired by Maxwell, he grew soulless bodies from scraps of his own Hell-gifted flesh. These smote birds, sought old bones, and toppled the cairns that marked fallen rams. These they carried back to become further raw materials for the Lord of Tambelon's research on undeath.

His one mistake came when one of his clones discovered the body of a pony, fallen from a great height. Raising it and imbuing it with a degree of independence, Grogar took a risk and sent his new thrall back to the Valley of Dreams, that he might scavenge from the graveyards of equinity.

Unfortunately for him, Grogar had not accounted for the Royal Sisters. The mockery of a stallion felt foreign to sun and moon alike, and Celestia and Luna soon investigated it. The younger sister traced the strange, bleak magic to the land of the rams, where a fortress stood impossibly amongst the nomadic tribes.

Grogar sent messages to Luna, desperate missives that portrayed him as a harmless scholar, who sought only to expand the borders of knowledge. He even sent them by dove. Zombified dove, but he hoped the symbolism would hold. At the very least, it gave his clones time to evacuate Tambelon, taking numerous books and promising specimens with them, including the Black Codex.

Once Luna had recovered from disconcertion and disgust, she sent back the dove with her reply: "Are you willing to cease these transgressions against the natural order?"

The bird returned and, in its master's voice, answered, "I am not. And I am sorry." It then exploded in a burst of soul-draining negative energy.

The apology gave Luna enough time to defend herself, and she found the assault not nearly as terrible as she expected. The void of death was little compared to the true emptiness of space. With that thought, she enveloped the fortress in her magic. The stone would be little trouble, but teleporting another living being as far as she intended would be impossible even for her.

But there was not a single living soul in Tambelon.

With a single spell, Luna sent the castle and its contents out past the heliopause. Grogar's last living discovery was that exposure to interstellar vacuum was enough to kill him.

Most of his clones collapsed without his guidance, scattered throughout the Belon Ridge. His oldest, the ones guided long enough to gain a faint imprint of awareness and agency, continued on until they found someone who would accept their burdens. Many of Grogar's texts were destroyed by exposure to the elements, but those that found their way into willing hooves became the basis of modern necromancy.

Meanwhile, the Black Codex, wrought into existence by demonic will, feared not rain or wind. It waited for a new master for centuries. At the beginning (or near the end, or three squillionths from the middle) of the Discordant Era, the draconequus threw it into his bag of intriguing things. He placed it… somewhere. Not even he's sure anymore.

Once Grogar's mind died, it was drawn to his soul, in Tartarus. Normally, demons enjoy tormenting their soul-debtors, but Maxwell, Coldest Logic, took no such joy. He freed Grogar, inasmuch as any can be free in Hell. Now the Father of Necromancy wanders the Inferno, unable to truly kill, unable to truly die.

Grogar normally appears as he had in life, an underfed, blue-coated ram with horns of deeper blue, glowing eyes of solid red, and a mouth full of terrible fangs, twisted by years of channeling the power of death. He has an underbite, and his lower canines protrude like tusks. His horns glow as he uses magic, not with a surrounding aura as a unicorn horn, but glowing from within with twisting, writhing patterns of light and shadow.

When enraged or truly committed to destroying something, he sheds this affectation. His skin and flesh dissolve in lightless flame, and his bones grow enormous, reaching up to twenty feet in height. Each bone is inscribed with fell runes that cause it to glow like his horns, and the glow of his eyes remains in his sockets, contracting to pinpoints or expanding to fill the orbits as per his mood. He wears his own tattered pelt and burning corpus as a mantle. In this state, he can become intangible at will, like the ghost he is, able to pass through walls and still slam a hoof down on those who so displeased him as to make him assume this dreadful form.

Grogar hates ponies. He will lash out at any he sees, eager to snuff out their souls. Zebras awaken what little compassion remains in him, for he still remembers the tribe that started him on his path. Others he takes as he finds, courteous to those who do not charge him as soon as look at him. He has gone through the cycle of insanity and restored mental stability more than a few times over his afterlife, and as such can now only be called differently sane. Approach with caution.

2813622 I still like my headcanon of Tartarus being an island made into a prison, but this is creative!

2813622 Do you mind if I use this? I've been meaning to make a Tartarus fic, and this would make everything so much easier.

2814633
As long as you credit me for the original idea, go right ahead!

2815372 Will do. It'll take a while, I like to plan things out, but I like this idea.

2815418
Awesome! Send me a PM when it's done.