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Greyhawk Deity
Ilsensine the Great Brain.
Title(s) The Great Brain
Home Plane Concordant Opposition
Power Level Greater
Gender Sexless
Alignment Lawful evil
Portfolio Mental Dominion, Magic
Domains Evil, Knowledge, Law, Magic, Mind
Superior None

Ilsensine is the god of Mental Domination and Magic, and the patron deity of illithids (also known as mind flayers). While not the creator of illithids, Ilsensine sees mind flayers as the entities most worthy of dominating the universe. Its symbol is a brain with two tentacles, or a stylized illithid face with four tentacles, rendered in jade green. Sometimes this face is depicted clutching a planet in its tendrils in the same way a mortal illithid might clutch the skull of one of its victims before extracting its mind.


Ilsensine appears as an enormous emerald-green brain trailing thousands of nerve ganglions off into the distance. Ilsensine is obsessed with gathering knowledge of all varieties, and its ganglia stretch to every corner of existence, tapping into all the knowledge of the universe.


Ilsensine cursed the derro god Diinkarazan and seeks vengeance against Diirinka, who successfully stole from it. It was formerly served by the illithid god Maanzecorian, who was recently killed by Orcus.

Ilsensine is an enemy of Lolth and Laduguer, but is allied with Kiaransali. Ilsensine's relationship with the dwarf god Dumathoin, whose realm overlaps the brain god's, is ambiguous but nonhostile. Dumathoin's and Ilsensine's mortal worshippers do not share this nonhostility, making war with one another as often as mind flayers and dwarves typically do, which is essentially whenever they encounter one another.


Ilsensine dwells in a series of caverns beneath the Dwarven Mountain in the Outlands called the Caverns of Thought, along with a vast army of mind-controlled thralls. This realm is intertwined with that of Dumathoin and that of Gzemnid, which stretches near the gate-town of Glorium.


Ilsensine is a cold and calculating activity that embodies mental prowess, the pursuit of knowledge, and absolute domination over all other life. Ilsensine demands that mind flayers enslave and ultimately consume the "cattle"—all other races—that surround them.


Ilsensine is served by illithids, cranium rats, and eaters of knowledge, and it is the patron of all who enslave the thoughts of others. Because Ilsensine promises power and domination to all that follow it, sometimes members of other races (particularly psions) will create small cults devoted to the deity.


Illithids do not worship Ilsensine in the same way that other races typically worship their gods. They revere Ilsensine because it—as an all-knowing disembodied brain—epitomizes everything that their elder brains aspire to be, and might one day become after evolving for uncountable aeons. The mind flayers envy Ilsensine's knowledge, supplicating it and entreating it for favors, but the illithids are too self-centered to truly worship anything.

Ilsensine generally sends a thought slayer as its herald. It is also served by a powerful proxy, Lugribossk. Its planar allies are succubi, mariliths, and cerebrilith demons.


The priesthood of Ilsensine is small and selective. They revere knowledge for its own sake, living in monastic temples isolated from the rest of mind flayer society. They are respected by their peers (unlike illithid wizards, who are reviled), but rarely envied, as Ilsensine's servants must give up the privilege of having their brains join the community's elder brain after their deaths. Instead, their souls belong to Ilsensine, and join it in its otherworldly realm.

Ilsensine's priests sometimes use cranium rats as spies and messengers. Some have levels in the cleric class, but many do not. Sometimes they can be seen moving silently through their communities on unknown errands; other illithids do not understand their motivations or activities, but in most communities they are not questioned, and receive the sanction of the local elder brain. They provide a measure of divine healing to their fellows, and are often slavemasters of both the living and undead.

Ilsensine's clerics are rare enough that each receives one-on-one instruction, as if from a master to an apprentice. Novices are often treated as little better than thralls until they prove themselves.

Ilsensine's favored weapon is the tentacle. Other races who follow the god substitute the unarmed strike.



Temples of Ilsensine are typically small, out of the way shrines in a nondescript corner of the illithid community. Larger ones may feature at the end of long, gently curving halls a stone idol depicting a massive, disembodied floating brain trailing long ganglia. The stone ganglia intertwine in complex knots before seeming to crawl up the room's supporting columns and merging with the ceiling.

Braziers of incense fill the air with the cloying, stinging scent of spice. Chambers attached to the main temple house the clerics and acolytes.



Illithids enter Ilsensine's temples when the idea of making sacrifices or requesting boons from the deity strikes them, although their society does not require they do this with any regularity, or at all if they do not choose to.

Mind flayer clerics seldom leave their temple complexes, though on rare occasions they may parade through their community's central plaza or select thralls and captives for ritual or scientific use.

Ilsensine's followers pray to it telepathically, holding their tentacles completely still as a sign of respect. When a particularly tasty brain is consumed, illithids dip their fingertips in the cerebral fluid and trace Ilsensine's symbol on a nearby surface.


  • Baker, Rich, James Jacobs, and Steve Winter. Lords of Madness. Renton, WA: Wizards of the Coast, 2005.
  • Cordell, Bruce R. Expanded Psionics Handbook. Renton, WA: Wizards of the Coast, 2004.
  • -----. The Illithiad. Renton, WA: Wizards of the Coast, 1998.