The King in Yellow
Most know the King in Yellow from Lovecraft's stories and the Cthulhu mythos in general, but it predates his stories by quite some time. The King in Yellow is a forbidden play which causes those who read it to go mad, and comes from a collection of stories by the same name written by Robert Chambers.
Along the shore the cloud waves break, The twin suns sink behind the lake, The shadows lengthen In Carcosa. Strange is the night where black stars rise, And strange moons circle through the skies, But stranger still is Lost Carcosa. Songs that the Hyades shall sing, Where flap the tatters of the King, Must die unheard in Dim Carcosa. Song of my soul, my voice is dead, Die thou, unsung, as tears unshed Shall dry and die in Lost Carcosa.