Illithid

The Illithid were a squid-like race who once ruled over the spheres. They are the oldest advanced ancient race known to historians, though the remnants of their civilization can prove difficult to find given the ravages of time and a culture mired in the occult and secrecy.
The Illithid lived more in The Dream World than the waking one, building empires of the mind in the same way that later civilizations built them across the spheres. While their technologies and customs are ill-understood to today's residents of the spheres, those who glean insight into their eldritch ways can commune with significant and dangerous powers.

History

Little is known about Illithid history, as they maintained most of their records inside The Dream World. Some accounts reflect a history that stretches back to the beginning of civilization itself on the spheres. Even during the time of the Geit Saints, the first organic civilization to take hold in the spheres, explorers from Jotun encountered Illithid who already possessed a deep understanding of dreams. The Illithid also left obelisks containing creation myths involving the Forger who created the spheres, suggesting at least second-hand contact with him and his shapers before his imprisonment.
The Illithid first arose on Io's moons. Their varied environments likely produced a diversity of culture and thought amongs their people that no doubt spurred an insatiable curiosity in understanding the mind that proved both their triumph and undoing. They soon spread across the spheres, colonizing settlements that spanned from the inner system to the Rim.
Archeological findings show no records of other contemporary civilizations who challenged their reign. Even without competition, their spread was more diasporic than continuous, leaving large tracts of territory untouched. Illithid used teleportation and astral projection to unify distant settlements, developing most of their infrastructure in The Dream World. They only invested as much in the Waking World as necessary to provide sustenance and shelter to their physical bodies, devoting most of their energy toward expansion and conquest of dreams.
Given the Illithid's proclivities toward secrecy and the paucity of a tangible presence throughout the spheres, the individual events in their history often remain ineffable and laden with paradoxes. Several surviving records speak of a great flood that occured at roughly midway through their history--that somehow occured across all the spheres. Archeologists have found arks beached on Io's moons or even stranded amidst The Dream World's astral seas that presumably ferried refugees from this event. However, like much that occupied the Illithid, few physical markers remain to explain the origin or causes of this mysterious event.
Illithid expansion into dreams reached a fatal climax when they discovered and colonized an organism known as the Grave on the Ioan moon, Nimbus. A towering piece of coral that feeds off the psychic residue of artifacts and ruins, its constant dreams created a supporting stretching deep into The Dream World. The Illithid built laboratories and settlements within the Grave, using them as a staging ground for expeditions further into The Dream World than they had ever dived before.
Their actions awoke powerful enemies. The Dream World's strongest and oldest occupants, known as The Reikeh, struck back and wiped out most of the Illithid's civilization in The Dream World. With the locus of their civilization and power fallen to hostile forces, the Illithid were left with only scattered outposts in the Waking World. Their civilization whithered away before they ever managed to rebuild for a counter-attack, putting an end to the civilization who probed deeper into dreams than any other to inhabit the spheres.

Technology

Illithid technology is--unsurprisingly--shaped by their preoccupation with The Dream World. They were said to create entire planes from the fabric of dreams, erecting wonders and cities that far surpass any ever seen in the Waking World, as imagination and thought are always faster and more capable than the most skilled masons. These wonders came at the cost of transience, and many of their great demi-planes only persist in the faintest imprints of vague and unknowable descriptions in literature and art.
However, their expansion into The Dream World has resulted in leaving behind some wondrous artifacts unlike any created by other civilizations. Most Illithid technology is so foreign from the understanding of modern engineers that it is indistinguishable and synonymous with magic. Psionics, telekinesis, teleportation, invisibility, and curses were all commonplace to the Illithid--even if no one alive on the spheres has the faintest idea of how they accomplished them. Part of their success in these endeavors stemmed from working materials only found in The Dream World. For example, an unstable substance called Warp, allowed illithid to unlock the power of teleportation. However, the secrets to many of their techniques remain unknown even to the foremost experts on the Illithid civilization.
The Illithid likely did not use their artifacts in the same ways that modern civilizations who find them do. While creating a barrier of telekinetic energy or picking up a boulder using only one's mind might seem to us like powerful miracles capable of turning the tides of a battle, to the Illithid such feats would have been considered menial labor reserved for society's lowest ranks. If one were able to travel back to the time of the Illithid, they would likely be far more impressed with a clever piece of rhetoric or catchy song than any wondrous feat of engineering from civilizations ancient or contemporary.
Another area in which the Illithid displayed inexplicable gifts is the creation of life. Several mysterious beings the Illithid imparted the gift of sentience still occupy the spheres to this day. For example, their World Whales inhabit every major sea on the system, wandering as they update their nautical charts with new landmarks or artifacts and imparting such knowledge to any lucky enough to encounter them. The Grimoires are books the Illithid created with the ability to modify their own contents. They can still be found flying about the astral plane, or occasionally the waking world, adding to their knowledge about the subjects they were created to study.
Perhaps the most fearsome creatures that the Illithid created are the abominations. They were born from a symbiotic species of the Grave called the Grave Kepers, who wandered the ruins of the spheres to collect ancient artifacts to feed their mastered. Originally benevolent giants to any who did not interfere with their task, some became corrupted when the Illithid seized control of the Grave. Whether this was an accident or a deliberate act to bolster their ranks in their invasion of The Dream World remain unknown, but any who encounter such creatures on the spheres today should expect an encounter with a deadly foe.

Culture

The Illithid's culture was one marked by equal parts curiosity and paranoia. Dream World powers that only a few possess today, like reading thoughts or mind control, were commonplace among the Illithid. If you had enemies or rivals in Illithid society--as most did--you could never be certain your thoughts were secure, or even your own.
Physical violence, under any justification, was considered the domain of only the most uncultured barbarians--the last resort of savages whose minds were too feeble to face their adverseries through any of the accepted methods of persuasion, manipulation, or deception. Warfare--to the extent it could be called that--was more likely to be waged through mass hallucinations or a piece of art laden with subliminal messages than the deployment of troops across battlefields.
Throughout any era, dreams and The Dream World remained the cornerstone of illithid civilization. Astral projection and the ability to enter dreams were so commonplace that Illithid nobility hosted fetes inside their own dreams--showing off their fancies or ideas the way a Homyn countess might display pieces of art. Of course, inviting one's rivals into your subconscious opened risks for intrigue and subterfuge, but most saw this as a necessary risk to keep up appearences and climb the social ladder in the Illithid's endless struggle for mindshare.
As denizens of The Dream World, the illithid had frequent contact with Daemons. Their relationships with them were as varied as the relationships other civilizations shared with foreign worlds they colonized. Some, the illithid enslaved for their own purposes, others they enjoyed cordial and formal relationships with, while others still actively resisted Illithid entry into their demi-planes.

Legacy and Artifacts

Illithid artifacts are rarer than those of other major civilizaitons that inhabited the spheres owing to their smaller footprint in the waking world. Those that do find their ways into the hands of Corsairs are often as potent as they are strange. Illithid artifacts are also the most likely to be cursed, sometimes as means of protection but also at times necessary enchantments to counterbalance an artifact's powerful effects.
Over the course of their adventures, the party has come across a few remnants of Illithid civilization:
Artifacts-- Illithid Gauntlets , Illithid Vanishing Cloak, Warp Rifle, Warp Staff, Grimoire of Figments, Golem Battery.