Hastur, also known by his epithets The Unspeakable One and The Yellow King, is a deity of H.P. Lovecraft's Cthulhu Mythos. Originally the creation of Ambrose Bierce in his short story, "Haïta the Shepherd", where Hastur was a god of shepherds, Hastur is also the name of a city in Robert W. Chambers' short stories, "The Yellow Sign" and "The Repairer of Reputations", both of which appeared in his short story collection, The King in Yellow. Hastur is later mentioned in Lovecraft's "The Whisperer in Darkness", however it is uncertain as to what he's being referred to as. More recently, Hastur has appeared in August Derleth's additions to the Mythos as a full-fledged Great Old One and half-brother of Cthulhu.
Powers and Stats
Tier: Unknown, Likely at least 4-C if not Higher.
Name: Hastur the Unspeakable, The Unspeakable One, Him Who Is Not to be Named, Assatur, Xastur, H'aaztre, or Kaiwan, The Yellow King
Origin: Cthulhu Mythos (see note below)
Gender: None. Referred to as male.
Age: Primordial, likely as old as time.
Classification: Great Old One, Deity, Eldritch Abomination, Half-Brother of Cthulhu
Powers and Abilities: Superhuman Physical Characteristics, Flight, Insanity Inducement, Mind Control, Reality Warping, Shapeshifting, Regeneration (Likely at least Low-Godly), Immortality (Types 1, 3 and 4), Telepathy, Possible Higher Dimensional Manipulation, Eldritch Physiology (is composed of matter not of this universe), Avatar Creation
Speed: Unknown, likely at least Massively FTL+
Lifting Strength: Likely at least Class T (His half-brother Cthulhu is described as "miles high", which may or may not be hyperbole. Hastur should be of comparable stature)
Striking Strength: Likely at least Class PJ
Durability: Unknown, likely at least Star level
Stamina: Unknown, but likely very high.
Range: Several kilometers physically, likely Planetary with Reality Warping. Possibly Universal with Telepathy.
Standard Equipment: The play, The King in Yellow, located on Earth is somehow connected to him.
Intelligence: Possesses a high degree of cosmic awareness if not nigh-omniscience.
Note: Hastur is not canon to the "original" Mythos created by Lovecraft himself and is simply a later addition by Lovecraft's literary executor, August Derleth.