There is more than one author with this name
Gregory Hill, also known by the pen name 'Malaclypse the Younger' (Mal-2), was one of the two writers of the Principia Discordia, along with Kerry Wendell Thornley (aka Lord Omar Khayyam Ravenhurst). He was also adapted as a character in The Illuminatus! Trilogy. During the early years of circulation of the Principia Discordia, rumors claimed that the author of the book was Richard Nixon, Timothy Leary, or Robert Anton Wilson; or that the book and Malaclypse the Younger were both fictional inventions of Robert Anton Wilson, as with Abdul Alhazred's Necronomicon.
Robert Anton Wilson stated, in the lecture "The I in the Triangle" from 1990, that Greg Hill was at the time the head of a large computer facility owned by one of the largest banks in the United States.
Greg Hill described Mal-2 as a spirit sent into him by Eris that helped him write the Principia Discordia over the course of ten years in his early adulthood. An interview included in the fourth edition of the Principia Discordia by Loompanics Press reveals that Mal-2 left once the book was finished. He claims Mal-2 returned to leave a fifth and final edition consisting solely of a Western Union telegraph form filled with the letter "M". Greg Hill also reveals that he had access to Western Union forms when he worked at Western Union.