The King in Yellow

Not much is known about the King in Yellow. Some claim he (if such a being is a 'he') came to Earth when it was young and built first a castle, and then a city. The city is mentioned in some sources as being called Carcosa. This castle & city was originally present when Earth was of one supercontinent, and when early man first appeared it was drawn into a pocket dimension, though some think there is a portal or other method to get to it somewhere in the world. A few believe that the city lies deep in the Underdark, and can be visited by those who know where it is.
The King in Yellow is a being that is not fully understood, with him being described as wearing hooded yellow robes. He is rumoured to have touched the mind of a creature with the ability to write prose of astonishing beauty and twisted their ability to write. The resulting play that this creature wrote drove it insane, and anyone who reads it finds the 1st act driving them into utter despair, while by the 2nd act, their mind has snapped and driving them utterly insane. Scholars who have knowledge of this point to it only having three acts, and no-one has been able to finish it. Anyone reported to have finished it has disappeared never to be seen again.
Also, the Kong in Yellow has been tied another accursed book called the Necronomicon, which mentioned the King, referring to him as Hastur. Both beings seem to be able to drive mortal beings to extremes of insanity and depression, and can be summoned by mortals, with cultists rumoured to be worldwide. The King in Yellow is mentioned by some to be humanoid in shape, yet moves in ways that no mortal humanoid can, all the while moving extremely gracefully, and with the poise of a professional stage actor. At the same time, the voice the King uses ranges from a whisper to a loud, booming voice, sounding both masculine & feminine in perfect unity. On rare occurrences this voice changes between both, and sounds opposite, again at the same time. An air of other voices seem to accompany him, with faint music too consisting of primitive bone & reed pipes, and skin drums, both rhythmically and atonal. These are faint enough that most don't hear it directly, and more like an irritant in the back of the skull. Rarely is the King in Yellow actually encountered, and most contact is made with his cultists who are quite unpredictable in their nature, and surprisingly aggressive when they encounter creatures in a position of power, or of another religion. Many are degenerate decadents.