"This city is the perfect breeding ground for minds of all kinds. I have no intention of wasting such a...fertile pen of intelligence."

Extremiton is a rare form of illithid known as an Ulitharid, a Mind Flayer who are treated as nobles among the aberrations. It led the remnants of another mind flayer colony to the surface long ago, tasked by its former Elder Brain to establish a new home for them. Finding this home in the Seadeeps located on the 17th level of Undermountain, Extremiton rebuilt its colony to become an Elder Brain itself in time. Having secured a dragon, it sought to become an Elder Brain Dragon, a twisted and depraved creature that would allow it to conquer other levels of Undermountain while reigning supreme among its kind.

However, as the mind flayers built their colony Extremiton grew fascinated by the beings that resided in Waterdeep above. Using its heightened telepathy, it communicated with the minds above having grown intrigued by the complexities of life in the city. To experience it, it built a series of psipods under the colony, devices that could imprison sentient creatures in a Dream version of Waterdeep known as Alterdeep. Crafted from information gathered telepathically from Waterdavian's minds, Extremiton would enter this simulation as an illusion of characters to further its fascination with the city. Among its favored characters, Durnan was its preference as the bartender appealed to the illithid due to his gruff yet caring nature to all the residents of the city. Extremiton's experiences with these beings' state of existence allowed it to achieve almost feelings of humanity, viewing the city as somewhat worth defending both for amusement and also tactical advantage toward it's goal.

This fascination subtly influences the rest of Extremiton's colony, with the other illithid sharing their ulitharid's curiosity as his intelligence grows from the canvas of psychic experience at their disposal. Nihiloor, a Mind Flayer under Extremiton, was tasked with breeding intellect devourers to spread spies throughout the city while working toward abducting more individuals for the Mind Flayer colony. Nihiloor has served as the liaison to the colony under the Xanathar, extending the reach of Extremiton as the mind flayer enthralls victims of the city for their own uses. Despite their low numbers, Extremiton's influence caused many in the colony to grow into Mind Flayer Arcanist, reinforcing their smaller numbers through arcane knowledge gleaned from their victims. 

This would prove a necessity when a Githyanki group learned of their influence in Undermountain, establishing their outpost on Level 16 in the mega-dungeon. Making war against the Undermountain residence, the githyanki have been on the offensive in keeping Extremiton from influencing the other levels while hindering Nihiloor in gathering new allies to join the mind flayer colony. Alongside this, the Gang War in Waterdeep above has caused Extremiton to withhold its transformation into the Elder Brain Dragon. With little option, Extremiton has bred a Neothelid as a contingency to wipe out its githyanki opponents. Aware that once the creature is unleashed it would be a matter of time until it turns on its creator, Extremiton seeks a way to resolve the conflict above to aid his efforts below. Nothing matters more to it than its fascination with the world it cannot be a part of, no matter how many suffer in its wake.

Personality

"You look upon me and see a monster to be slain. I am an intellect beyond your comprehension, but I seek to know yours. However minor it is."

A contrast even among its own kind, Extremiton is a strikingly friendly ulitharid to life it encounters whether it be in the psipod simulations or telepathically above. It harbors a fascination toward those that get its attention, their free will a stimulating feeling in the being as it seeks to learn all it can from those it keeps hostage or going about their lives. Extremiton uses his colony to expand his fascination with non-illithid kind, the manipulative being not interested in conquest like its species but a newfound desire to experience life in all its steps. Due to its illithid nature, however, Extremiton will always be unable to fully empathize with the emotions of those it keeps victim, a revelation that deeply affects the already deviant being among its kind.

Despite this empathetic appearance, it is ruthless in managing the other mind flayer seeing them as canon fodder to its own goals. In its mind, they are all subservient to it because of its own pursuits and lack any free will like it has, having grown attached from the lives it has absorbed in Alterdeep. While it won't deny its desire to become an Elder Brain Dragon in the end, Extremiton finds other species more fascinating than its kind in most aspects. This has led to the little reason to expand its colony in Undermountain despite their smaller numbers, only needing enough mind flayers to keep its operation running under the city. In fact, the creation of the neothelid highlights this viewpoint immensely since the creatures are viewed as abominations by the illithid kind. Yet Extremiton made one purely as a weapon to unleash against his enemies, despite the toll on expanding his colony from the creation it would take.

Extremiton believes its actions are justified in its isolation, for rather than outright devour Waterdeep's people it views the place as the perfect breeding pen to satiate its desires for knowledge or brains. While it has no interest in playing hero or managing the politics of the city above, it will use its telepathy to control one of the spies above for its own purpose separate from the colony. Often this takes the form of some Noble Prodigy, Guard, or any rank of Commoner. When dealing with others to mask himself, he will use children as useful thralls as they serve as a tactical shield against those that would do it harm. Nihiloor itself has acted on behalf of Extremiton, the mind flayer serving as its eyes, ears, and even voice when the ulitharid seeks to exert its will on the population.