The illithid empire held many worlds and even a few planes of existence in their tentacled grip. Long ago, before many of the worlds known in the present day were born, the illithids ruled a vast empire known to some as Nihilath. For example, gish'sarath combines the word gish, or 'skilled,' with sarath, or 'sergeant.' Githyanki who have trained with great heroes add the prefix gi' ('student of') to their trainer's name.

In the githyanki language, apostrophes (which are not pronounced) separate different morphemes which have been combined into a single word. They also speak Common, and many speak Draconic. Githyanki have their own language, much like that of their cousins the githzerai, commonly known as Gith. The worship of gods is forbidden in githyanki society, and because they often make their homes on the floating, stonelike corpses of dead gods drifting in the Astral Plane, they aren't very inclined to piousness in any case. Non-evil githyanki are one-in-a-million exceptions, and good githyanki are unheard of. Githyanki are almost always evil, though they can be chaotic, neutral, or lawful. Their black eyes are sunken in their skulls, and their ears are pointed and serrated in back. They have leathery, pale yellow skin, and red or black hair. Githyanki are vaguely similar to humans in appearance, but taller and much gaunter, averaging six feet, three inches tall and weighing an average of 170 pounds.

They have fortress-outposts on many planes and Material Planar worlds, expecially near illithid lairs, as well as brood-chambers to incubate their eggs. Their fortress-cities are built on chunks of Astral stone or on the titanic stony corpses of dead gods. Githyanki are considered to be native to the Astral Plane, though their distant ancestors were humans from the Material Plane. Because biological processes temporarily stop for those on the Astral, the githyanki must travel to other planes to breed, normally the Prime Material Plane. Unlike their mammalian ancestors, githyanki reproduce by laying eggs.

R dawn of war