"The King in Yellow" is a book of horror short stories written in 1895 by Robert W. Chambers. The first two chapters of that book are the manuscript of a fictional play by the same title. Some accounts claim that the play was not fictional, but was the work of an unknown female playwrite who went mad and hung herself while penning it.
Having never read the book and only knowing the general story of the play from a short synopsis he'd found, Ythill decided to temp fate and rewrite the tale as a screenplay. Shortly after he finished it, his (now ex-) girlfriend deleted it out of spite. Luckily, Ythill neither went mad nor killed himself, though he seriously considered choking her.
One of the original antagonists of the story was an otherworldly magician named Ythill. He was also known as The Phantom of Truth for he could not lie. His visage appeared to be a mask to others though it was his real face.
It is from this source that the name originates. You'll have to figure out everything else on your own.
Ythill is the go-to source for locating porcuporn.