He is a being of power unimaginable to mere mortals. The very sight of him drives mortals mad. On 2012, at the rise of the Gibbous moon, on the end of the Mayan Calendar, he will awaken from his slumber and teach man a new kind of fear. He will arise from the lost city R'lyeh in the furthest Reaches of the sea. His spawn are the foul deep ones, smaller versions of the great one and the people of the lost city of R'Yeh. A place with structures built with non-euclidean geometry, the very likes of which cannot be imagined by mere mortals, and to lay eyes on it is to be driven to the depths of Insanity. His cult is centered in Arabia, with members all over the world, from Greenland to Chile. The leaders of the cult hailing from China. Among the Great Old Ones his main rival is his half brother Hastur.

A famous phrase about cthulhu is "Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn" which roughly translates into "In his house at R'lyeh Dead Cthulhu lies dreaming". He inspired the mad Arab Abdul Alhazred to create the Nercronomicon, a book bound in human flesh, the pages made of skin, and the words written in blood, that describes many gory rituals to awaken the great old ones and describes them in horrific detail. Perhaps the most famous Couplet from it is " That is not dead which can eternal lie.

He has many minions, not the least of which are the horrific Deep ones. He has divine servants such as Dagon and Hydra, though it is debatable whether or not that they are Divine or simply just really large Deep ones. But his favored minions are The Star spawn of Cthulhu, also known as the Cthulhi, they are like Miniature versions of their great and dark Master. Cthulhu's Consort is Idh-yaa and she bore him four children. In order from oldest to youngest they are, Ghatanothoa, Ythogtha, Zoth-Ommog, and Cthylla. The first three being his sons, and the last being his only daughter.     Cthylla is guarded by deep ones and far worse creatures as she is vital to the Great one's plans.  For if Cthulhu is ever to be destroyed beyond his healing factor's ability to repair, she would give birth to him again.   

He has power beyond mortal comprehension and is able to nearly instantly regenerate his body if it is ever to be damaged the wound will heal faster than it is made.   He is the ruiner of countless worlds, the devourer of innumerable souls, and ender of hope.    He also has immortality beyond what most can comprehend, for it is stated that he will outlast death itself.   If this is true then he can never be truly destroyed.    He is as large if not larger than any earthly mountain, being able to stand well above sea level in some of the deepest parts of the sea.    It is unknown whether or not he can fly using his massive wings, but it is probable.       He is also capable of shape shifting, as he has taken multiple forms over the years, one the Octopus headed, Dragon winged, Human caricature that is the most familiar.  Another a gigantic pulsing blob of writhing tentacles and mountainous pseudopods.   Another a huge mass of constantly changing colors.    All will cause a man to go insane upon glancing it.      

In fact Cthulhu's power is so tremendous that when he is to awaken everything in 1,000 miles of R'lyeh will either be destroyed in mind, body, and soul which is the fate of the more fortunate ones, or go irrevocably insane as you see the truths of the omniverse.        Unlike most beings who are limited to one multiverse, Cthulhu exists in the Dungeons and Dragons multiverse as well as the Lovecraft mythos at the same time.       His mastery of magics, technology, and psionics have few equals anywhere in existence and the simple fact that he has mastered all three of these rather than just one is truly a feat.      He also is capable of reality, matter, energy, time, and space manipulation on a truly massive scale.   His age is stated to be in the vigintillions of years, or 120 or so Zeroes.   Thus making him vastly older than the universe is predicted to be or even is predicted to last, thus implying that he has seen many many universes come and go and that ours is merely the latest one to him. 

More of his powers include, the ability to ignore nuclear weapons as if they were nothing, knowledge and mastery of every single spell, and much like the vast majority of the great old ones, is able to summon Azathoth with a spell that has the energies to destroy worlds.    Azathoth is the ruler of the outer gods, beings above the Great old ones and equals of the Elder gods in the books of August Derleth.

His resources also are practically endless like his power.   He has an army of truly massive proportions at his disposal, consisting of untold legions of insane horrors all over the multiverses he exists in.    R'lyeh was merely the tip of the iceberg of the resources at his disposal, so to speak.   As mentioned he has mastered sciences Man kind has never seen, and he has mastered magics well beyond the reach of any man, and his control over psionic forces has few peers.  Thus furthering his resource pool.    His allies are many and his enemies are few.   For who would in their right mind challenge something that is madness incarnate?   

While he has only starred in one book of Lovecraft's stories and has been merely a minor monster in his books, other authors soon increased his powers, from a Godzilla level to a Galactus Level entity in a few decades.  He has spawned perhaps the most spin offs and rip offs of any Fictional Entity in existence.    Shuma Gorath, The Illithids, Aboleths, and Elder Evils of Dungeons and Dragons, The Nameless things of Tolkein, and Virtually every madenning thing of a near unknowable age.