The eponymous character in Haita the Shepherd by Ambrose Bierce.
Interestingly, Haita is Gothic for "I call" - potentially fitting if Hastur is derived from the Visigoth settled Asturias. Given the similarities to an Old Testament prophet, it would suitably recast the title as "I call the Shepherd". Whether Bierce was aware of the word or whether this is a happy coincidence is unclear.
Although not mentioned as being in the play, his presence would not be out of place. He has a role in The King in Yellow (Scott translation).