Character created by H.P. Lovecraft. "Messenger and soul of the Great Old Ones" (he was also frequently associated with a nebulous set of Other Gods - possibly to be identified as the Great Old Ones or Outer Gods, and was also a protector of the Great Ones, the gods of Earth's Dreamlands and antiquity). Said to have a thousand forms: The Encyclopedia Cthulhiana hypothesizes that King in Yellow could be an avatar of Nyarlathotep rather than Hastur. In Fungi From Yuggoth he is described as wearing red and is implied to be the messenger of Azathoth. In his form as The Black Man he is depicted as being totally black in colour.
In Ivy-Covered Horror he is described as the servant "of his bloated space-demon master Hastur". He is associated with the yellow-robed Last Elder One and the Black Pharaoh of Egypt. Possibly somehow connected with Lin Carter's Triple God of Chaos.