Slaanesh is the Dark Prince, the Prince of Pleasure, the Lord of Excess — youngest and in some ways most terrible of the four Ruinous Powers. Slaanesh is the god of hedonism, of sensation pursued past all reason, of pleasure and pain refined until the two become indistinguishable. Where the others are ancient beyond reckoning, Slaanesh was born in a single cataclysmic instant, and its birth-scream tore a wound in reality that endures still as the Eye of Terror.
For the Dark Prince was midwifed by the decadence of the Aeldari, whose ancient empire collapsed into an orgy of depravity so profound that it coalesced into a new god. In that birth the Aeldari were all but annihilated in the Fall, and to this day their souls are the sweetest prey Slaanesh hunts — a debt of terror that shadows every survivor of that shattered race.
Slaanesh craves experience above all: every sensation tasted, every perfection attained, every desire indulged until it consumes the soul. Its sacred number is six, and its daemonettes lure mortals to ruin with beauty that scars the mind. Among the Dark Prince's chosen are the Emperor's Children, the Legion of Fulgrim who pursued perfection until perfection damned them. To follow Slaanesh is to burn ever brighter and briefer, forever chasing a satisfaction that, by the god's cruel design, can never truly be reached.