a.k.a. Him Who Is Not To Be Named, the Unspeakable, the King in Yellow
A Great Old One of the Elder Mythos, dedicated to Decadence, Disorder, and Nihilism.
Referenced by Avros Setrakian in Ulver Zandalus' ecclesiastical record.
In Chapter 21, Gull had faint memories of him, thinking of him as an imprisoned being, perhaps trapped somewhere but still able to reach out and touch the world. He knew that cults dedicated to the King in Yellow exist in Golarion, and Dora thought of them as somehow being associated with decadent acts of bloodletting happening during public events of high culture (plays, operas, or the like).
In Chapter 29, Dora recalled that the Tatterman was one of his notable servants.
In Chapter 39, the party began to understand that the star stelae and the nightmare city were tied to Hastur somehow.
First Reference: Chapter 18
Other Notable References: Chapter 21, Chapter 29, Chapter 39