Aetercerians

The Aetercerians are an ancient group of creatures that share many features with demons.    

Creation

When the gods were still figuring out how to create things one of the first creatures they created were the ones that would become the Aetercerians. They have a primitive form of soul, something that lacks the sophistication that the humanoid soul has but more capable than the soul of an animal. Initially the Aetercerians were living alongside the gods in the nothing. They would occasionally roam the worlds the gods were making, but since the gods weren't able to make intricate things yet there wasn't much for the Aetercerians to do there. There was one deity who subtly but intentionally altered the Aetercerians, causing them to become something like demons. As the creative power of the gods developed so did the power of the Aetercerians to interact with the creations. The Aetercerians started to destroy the things the gods made, leaving only what they felt were things they could rule over. Whatever the gods made, the Aetercerians degraded them to things that were essentially animals or slaves.  

Conflict

The gods decided they had enough of the Aetercerians messing with their creations. They wanted to get rid of the Aetercerians, but the gods weren't powerful enough yet to destroy them. Led by Heocanin, the gods repeatedly subdued the Aetercerians so that they couldn't interfere with the creations of the gods. However, this wasn't a permanent solution and required a lot of attention. Heocanin wanted to find a solution that would either destroy or pacify the Aetercerians for good. However, he was unable to pull his attention away from keeping the Aetercerians subdued and did not trust the other deities. Heocanin knew that he had to either get someone else to come up with a permanent solution or to take over the conflict. Pyurethoniam saw the struggles of Heocanin and offered his assistance. Pyurethoniam would temporarily take over as the leader in keeping the Aetercerians occupied so Heocanin could come up with a permanent solution. It worked for a moment, Heocanin ruled out destroying the Aetercerians and realized they needed a permanent distraction. But time wasn't on his side as Pyurethoniam had once again taken things to the extreme. He had taken the Aetercerians to the elemental planes in an attempt to keep them distracted. However, the Aetercerians enjoyed the destructive power of the elements a bit too much and realized the elementals were easy to rule over. Fearing a catastrophe Heocanin pleaded with Asjitéok, who had remained neutral, to help him create a new deity. Enticed by the challenge, Asjitéok helped Heocanin figure out how to do so, but took no part in the actual creation of the deity. Heocanin succeeded in creating a deity, who would later take the name Cipiurra. He hastily informed the deity of its mission, to create a permanent distraction for the unruly Aetercerians. Then he went back to take over from Pyurethoniam, who was overwhelmed yet intrigued by the destructive powers of the Aetercerians, taking the Aetercerians out of the elemental planes, back into the Nothing. But it was arguably ever so slightly too late and some Aetercerians remained in the elemental planes. There they were transformed, becoming part of the elements but not in the form of a creative power like the elements were initially used for, but as tools of destruction.  

Imprisonment

Cipiurra was eventually succesful in constructing what the deities called Aetercerem, the eternal prison. This earned Cipiurra the nickname "The Jailor", a name she found unfitting since she did refused any responsibility for those who inhabited her creation. The prison would be a perfect place for anyone inside as they wouldn't even realize they are in a prison. It was the perfect world of illusion where the Aetercerians had everything they needed to remain distracted forever. Well... until the prison broke.  

Unbinding

The Aetercerians remained imprisoned in the Aetercerem for aeons and the universe ignored it, or so everyone thought. The deity, who at the beginning of time had altered the Aetercerians to become demon-like, was still planning their liberation, their unbinding. The devils and demons who were at constant war were all powerhungry, a trait the deity would utilize. The deity sowed the idea amongst the devils and demons to break the Aetercerem and use the Aetercerians as most powerful allies. The Devils and Demons fought over the Aetercerem and broke it in the proces, starting an event known as "the unbinding". The Aetercerians felt something was wrong "like a splinter in their mind". They could sense an ever present "crack" in the perfect illusion they were living. One by one they would break free and attempt to free more of their kin. Some did indeed ally themselves with Devils or Demons for the time being. They did not stay on the same plane as the Aetercerem but spread to other worlds and planes like a plague. Alveïn knew he could not stop all of them so he focused his attention mainly on preventing the Aetercerians from spreading to Dwarven worlds. The Aetercerians took a liking to the Lands of Despair (Shadowfell) and made their home there. However, banishment would still send them back to Aetercerem.   On Aerlad they established dominions in which they enslaved conscious creatures such as humanoids. This enslavement was usually through a form of mind drain and mind control, though there were instances of less subtle forms of enslavement. Since Aerlad was still young, it wasn't difficult to degrade the newly created beings to something that could be subjugated.  

Allies of Shadow

When the Ancient Drow began to worship their new found gods they were threatened by the rest of the world who did not accept their malevolent ways. Facing banishment to the newly formed Depths they called upon their gods to aid them, but their gods did not interfere. However, the gods instead called upon the Aetercerians who dwelled in the Lands of Despair. The Aetercerians emerged through series of shadowbursts, eager to torment the world of Aerlad. Many Ancient Drow allied themselves with the Aetercerians, but some resisted and opposed them. Those that chose to ally themselves found Aetercerians assuming the role of general in great wars. Other Aetercerians were uninterested in allegiances, yet they were bound by the force that had once created them and now moved among the Ancient Drow. Though they were not allies, these Aetercerians did not interfere with the ambitions of the Ancient Drow, instead focusing their attention on the plethora of other races.  

Patheothul unleashed

As Aerlad was crumbling under the destructive force of the Aetercerians the gods decided to interfere. They all banded together in series of major battles that would eventually see the Aetercerians destroyed, imprisoned, or banished back to Aetercerem. The fight against Aetercerians was, like once before, not easy. Unable to reimprison them in Aetercerem, they instead accepted the possibility of banishing them again to the Lands of Despair or imprisoning them on Aerlad itself. Annoyed by the half measures that were taken and curious as to what might happen, Pyurethoniam brought his most precious creation to Aerlad. Patheothul, god of death, swept over the world destroying everything in its path. A merciless indiscriminate force of pure destruction more pure than the Aetercerians, Patheothul wiped the slate clean. It was only when the gods of shadow finally came down by themselves that he was halted. For the gods of shadow were cloaked in Darkness, that which hides in Nothing. Exillerated, Patheothul returned to his father who had been watching with the most profound pride that anyone had ever witnessed. The gods, humbled by the demonstration of utter destruction, learned from it how an Aetercerian could be destroyed. In the following moments of chaos, the deities of shadow led their new worshippers into exile, to the Depths, away from certain destruction. The gods had free rein to subdue the Aetercerians who were abandoned by those that had called upon them. The Ancient Drow who had stood against the Aetercerians were banished along with their guilty kin, no trial, just judgement.  

Current situation

Aetercerians are either imprisoned since that conflict on young Aerlad or banished. Some might have returned from the Lands of Despair and established dominions, but most of their actions are still met with interference from the gods.
Some Aetercerians have attained a deified status through worship by creatures drawn to their power or through promotion by a true deity.  

Behavior

Aetercerians like to rule over simplistic creatures. They will destroy society to a certain level, usually a tribal or animalistic level, and assume rulership.     Every kind of Aetercerian has their own method for subjugation.
Aetercerians like the Mentenarii simply drain the minds of the sentient creatures to a docile subservient state. Those enslaved creatures would have a significant part of their mental capacity removed and over time replaced. The part of the mind that once facilitated life in a society was reallocated to things like psionics and other magical capabilities. Those abilities would then be used for very animalistic purposes. A creature could use psionic powers to bash away someone that would encroach upon its territory, or use magical abilities to innately know that someone is on their territory.   Aetercerians like Propereons use a more straight forward approach they subjugate through perpetual torment. By keeping everyone completely dependent on them they ensured total obedience.   Finally there were those like the Imagisuins who would choose a few servants in who they recognized a part of themselves. They would amplify these characteristics to turn them into powerful malevolent warlords or terrifying monsters.