Hastur, the Unspeakable One, and Him Who Is Not to Be Name, is the half brother of Cthulhu, though he has no special love for his half brother due to the fact that they are opposing elements. Which is intriguing as this is a departure from classical elemental theories.
It is unknown what sort of entity Hastur is, but he is largely regarded as a Great Old One. He is also depicted in other inscriptions as a fallen Angel, a Duke of Hell, and the God of Shepards.
He is equal in power to his brother and has the ability to shrug off nuclear weapons, bring madness with ease, and has mastered every spell in existence, including the spell to summon Azathoth, which is quoted as having the ability to destroy an entire planet.
He also has the power of shapeshifting, having taken on the form of a human dressed in yellow garments, a vaguely octopus like creature, a gigantic reptilian humanoid with tentacles writhing all over its body, a pulsing blob of writhing tentacles, and further more.
His manipulation of the wind is so terrifying that he is capable of causing devastating hurricanes across the globe, even produce storms in the regions of space. Hastur is mostly addressed as the Unspeakable One, for those who are foolish enough to dare utter his name, will be met with an untimely and swift death. The victim himself will not realize he has been slain until it is too late.