Illithids are one of the most arrogant, cruel, mysterious, and alien races in the underdark. Their racial belief is that they are a race far superior to all others, anything else is at best a begrudged trader or at worst, food. Each illithid is highly unique from the rest of the colony, save the elder brain; which is a sentient conglomeration of previous illithid brains. Loyalty to the elder brain is paramount in a illithids life, betraying its decrees end in either exile, reprogramming, or death. Exiled illithids are marked in some way and treated with suspicion by each colony, their minds cannot be seen as clearly as those within the elder brains collective intelligence.
The Illithid is a grotesque being, roughly humanoid in form its torso and limbs are thin and gaunt, with mauve skin and a squid-like head, equiped with four tentacles. Their mouths are either in lamprey or beak in form (depending on what species they prey on most), and their eyes are white and utterly lacking pupils. This however does not impede them in any way, for they see entirely in darkvision. They also possess a fantastic auditory sense, although they have difficulty determining one sound from another.
Illithids are created through a process called ceremorphosis, each illithid start off as tadpoles hatched from eggs, the adult illithid hermaphroditically spawn thousands of said eggs two to three times during its lifetime, within a pool of brine built exclusively for that purpose. Each tadpole hatches within month and then spends ten months within the pool and is fed a mixture of brains and organs prepared by nursery attendants. They then grow inside a nursery vat until puberty at age 9-11, only a select few (around ten to twenty) survive, an elder brain eats weaklings at the bottom of the vat, and are considered candidates for full ceremorphosis. The next stage involves placing the mature tadpole illithid into the ear, nose, or eye of a , preferably, human host that has been subdued but remains alive. The tadpole will then burrow into the brain of the subject and consume all brain matter. Over the course of a week the tadpole will replace the hosts body on the genetic level altering the body to resemble that of an adult illithid. However, the new illithid is only an infant and must go through extensive learning and training in order to reach it's full potential. The exception of this is the incredibly rare Ulitharid illithids, which spend twice as much time as an infant, live twice as long, and tower over their brehtren at 7 to 8 feet tall. Upon ceremorphisis they are treated as prophets and become completely aware of their abilities in a matter of days. They generally rule an illithid colony under the elder brain, recieve various boons, and many diplomatic embassies from colonies not so blessed.
Illithids work together extensively in order to fuel their racial goal, blotting out the sun. They use their thralls in any manner imaginable to further this goal. Illithids have a begrudgingly shaky tolerance for drow and aboleths, however this is due to the vast cities and cruelty of the drow and the aboleths nearly impregnable aquatic fortresses. Illithids that practice sorcery are known as Alhoons (illithiliches in the common tounge) and are deprived the gift of being incorporated into the elder brain upon death. The mysterious Vampire Illithid is to be destroyed on sight if detected by a true illithid.
Illithids revere Ilsensine for its intelligence, however, their innate, overpowering egoism prevents any true worship. Ilsensine is essentially a fully realized elder brain, formless in being but whose ever reaching ganglia penetrate everything in the universe and all dimensions. It probes the cosmos in order to gain all knowledge for some unimaginable goal.
Illithids lack a spoken language of their own, instead they communicate telepathically between one another. They often learn various languages, and although they loathe spoken language, they find the ability to read texts from other races useful. They possess their own written language, known as Qualith, which is a record of pure psychic communications. Non-illithids take years to learn to read even simple texts in Qualith.
Illithids have a true name, which is unspeakable and more of a mental signature, and a name which is used for communication. That name varies greatly.