Slaanesh, also known as the Dark Prince of Ecstacy, is one of the four gods of Chaos Undivided in Games Workshop's Warhammer and Warhammer 40,000. He is the god of pleasure, passion and decadence, but also the god of perfection. Slaanesh, unlike his brothers, isn't technically male. Slaanesh's true form is female on the right and male on the left, with to horns growing from his head. However, he prefers to take the form most pleasing to the person in front of him. Like his brothers, his true form is based on his domain of the mind. Khorne is a bloody and violent warrior, Tzeentch is a creature that defies mortal logic, Nurgle is a bloated creature infected by millions of diseases and Slaanesh is the most beautiful creature one could possibly see. Slaanesh's followers are a mix of the perverted and depraved, but also of those seeking perfection. A chef seeking the perfect recipe, an artist who wishes to make the most beautiful work of art or a designer who wants to make the best clothes on the market, among others are some of his greatest followers.
On a side note, Slaanesh is responsible for the Fall of the Eldar in 40k, having killed most of the Eldar gods during that dark day, as well as many psykers (futuristic mages) across the universe. Slaanesh now feasts on the souls of the Eldar, leading the race to protect itself in many ways. One force of the Eldar, known as the Harlequins, is protected by the laughing god Cegorach himself, leading Slaanesh into many battles with the last Eldar god to possess both freedom and a complete body for these souls. Also, his name is a corruption of the Eldar term "Slaaneth". "Slaa" translates to "ecstacy" or "pleasure" while "Neth" translates to "lord" or "prince", hence his title of Prince of Ecstacy. However, the Eldar refer to Slaanesh as "She who Thirsts", unlike humans.