The White Acolyte
From Tatters of the King
The significance of this statement, if any, is unknown, but Umberto knows of the legend of Chaugnar Faughn, the elephant-headed god of Tsang who is said to await the coming of 'The White Acolyte'. What possible relationship there may be between Chaugnar Faughn and the King in Yellow is unknown.
Malcolm Quarrie has revealed that the followers of Chaugnar Faughn have been duped. It is the King in Yellow who awaits the White Acolyte, who will free him from the Upper House and take him back to earth. Quarrie hopes that he, himself, is the White Acolyte, but is unsure. It is possible that it is yet to be determined who the Acolyte is.