Slaanesh is the embodiment of obsession, excess, and unchecked desires, the patron of aesthetes, wantons, and all who would let their indulgences rule them. Its generally referred as male by humans as Prince of Desire, Prince of Excess and Lord of Pleasure, while its referred as female by the Eldar, who do not call it by name and refer to Slaanesh as She Who Thirsts, the Great Enemy and the Great Serpent. In truth, Slaanesh is neither both and neither at the same time.
Slaanesh came into existence when the Eldar, an ancient star-faring race that ruled the stars long before the Imperium's ascension, decayed into complete depravity and decadence, indulging in every vice and desire imaginable. This psychic energy gestated into the Warp from its depraved lust spawned Slaanesh, an new Chaos God that consumed the bulk of the Eldar race, their spirits sucked into the Immaturium to be forever tortured and defiled by the newly-made deity and absolutely destroying its empire. The epicenter of Slaanesh's birth became known as the Eye of Terror, a massive Warp rift that serves as an entrance into the Realm of Chaos.
Slaanesh's appearance defies description, for each viewer sees the embodiment of their most buried desires, a being of unnatural beauty that evokes arousal, adoration, and acquiescence. Slaanesh can take any form, and has been depicted as male, female, hermaphroditic, or androgynous, though a classic interpretation is of a figure split down the middle into both sexes. Mortals that seek charisma and fellowship turn to Slaanesh, for his gifts can make one popular and inspiring. Poets and artists are drawn into his gaze by the promise of inspiration and fame, while even the hardiest warriors might seek the adulation of the masses and the ironclad loyalty of their followers. It will give one sensations beyond their wildest imagination, pleasures and pain beyond understanding, which their warped body will eventually become acclimated to, forcing them to take increasingly extreme measures to reach similar highs, even as their senses become dull. Eventually they will be undertaking ever-more disgusting atrocities in an attempt to stir their jaded emotions, while they hardly feel anything at all.
Slaanesh is widely considered the weakest of all Chaos Gods, due to his worship being less widespread in the galaxy than other Gods. However, no mortal being can hope to confront it, for whoever gazes into Slaanesh will forever forfeit its soul and become its willing slave and plaything. Slaanesh's daemons possess what is called "Aura of Acquiescence" that compels mortals to bow down and worship their inhuman beauty, save for those with the strongest wills. Embodiments of the alluring power of pleasure, their very presence is enough to bring even the most stalwart warrior to his knees in anguish and ecstasy. Pain is simply another sensation to be bestowed upon others, or to be enjoyed when others inflict it, for all sensation is a blessing to Slaanesh. His Daemons feed upon the rampaging hope and the thrill of fear to be found within their enemies, as they feast upon terror and despair.
Khorne is regarded as Slaanesh's mortal enemy among the Chaos Gods, as the belief fighting and killing for its own sake to be the dullest affair if its not for pleasure. In turn, Khorne regards Slaanesh and his followers' obsession with luxury and torture wasteful and dishonorable.