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Game background
Title(s) The Great Brain
Home plane Concordant Domain of the Outlands
Power level Greater
Alignment Lawful Evil
Portfolio Mental dominion, magic
Domains Evil, Knowledge, Law, Magic (also Mind)
Design details

In the Dungeons & Dragons fantasy roleplaying game, Ilsensine is 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. 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. The Symbol of Ilsensine is a brain with two tentacles protruding from it.

Publication history[edit]

Ilsensine was first detailed in the book Monster Mythology (1992), including details about his priesthood.[1] His role in the cosmology of the Planescape campaign setting was described in On Hallowed Ground (1996).[2]

Ilsensine is detailed in the Expanded Psionics Handbook (2004),[3] and in Lords of Madness (2005).[4]


Ilsensine appears as an enormous emerald-green brain trailing thousands of nerve ganglions off into the distance. It is made of the brains of all the illithids who have died. Ilsensine is served by illithids, cranium rats, and eaters of knowledge.


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 later killed by Orcus. Ilsensine is an enemy of Lolth and Laduguer, but is allied with Kiaransalee.


In the Planescape setting, 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 Gzemnid, and stretches near the gate-town of Glorium.



Ilsensine is served by illithids, cranium rats, and eaters of knowledge.

Forgotten Realms[edit]

In the Forgotten Realms campaign setting, Ilsensine lives in the Deep Caverns.