Azathoth is a blind, insensate mass the size of a star, gibbering in the purported center of the universe in the Astral Plane. It is surrounded by satellite beings who make eldritch sounds like idiot flute players.
Those who approach Azathoth go mad. Those who worship it worship insanity, and they are themselves insane.
Deities & Demigods (AD&D 1.0, first printing)