The god of shepherds created by Ambrose Bierce. While Lovecraft did little but drop the name, August Derleth and Mark Schorer expanded his fame by explaining in "The Lair of the Star-Spawn" how "Hastur the Unspeakable" was a member of the Great Old Ones and was banished, when Cthulhu was exiled in R'lyeh, to Hali in the Hyades.

[The Whisperer in Darkness - H.P.L.]