The beasts rose in form of one tho i did raise shields of light...
Swords of darkness did impale my soul as i did cry out in pain
Destructive storms, winds of heralding bane cast me out
The circle of Cthah was formed in a name, shape and number
Veils of darkness did cloak my soul
Winds of fire did appear before
Ia Zi Annga Kanpa Maskim Xul
Ashen eyes did stare upon the earth
The skies did turn black yet once more
Into the dark waters we did fall as i did hear the name of the beast being that whom is Cthulhu...
As did i look upon the seas and called out in names of Xul.. Hearken lords of light.
—The Darkening Seas, Cephalectomy
The earliest proven mentioning of Kutulu is by Aleister Crowley. His Great Beast as represented in "CTHAH 666". The word Kutulu can be defined two ways...
Kutha-Lu: "man of Kutha"
Ku-Tu-Lu: "sleeping dark one" or "man of the sleeping dark"
This is from the spelling presented by the "editor" of the Necronomicon under the moniker "Simon" (in referance to the biblical figure Simon Magus). There are many varied spellings of Kutulu, such as Cthulhu, Cthhuhhlhu, Chutha-Lu, etc. The meanings are varied and the origins of most seem to be shadowed, leading me to believe that it all boils down to one source. The two possibilities present in my mind are Kutulu and CTHAH. Though I havent seen Kutulu in any Sumerian tablets to date, it seems like the most feasible option. The Crowley inception of the word may have evolved from this, as he did show interest in Sumerian culture. This would place CTHAH as the man of Kutha, the principle city where Nergal, the Sumerian underworld god, was worshipped. Some say that Kutulu would translate to “Kutha man” making “man of Kutha”, Lukutha. Either way, the meaning is clear. The Greek word Cthone refers to anything of the underworld (ie. 'Cthonic'). It is quite possible this is where Howard Phillips Lovecraft derived the name 'Cthulhu' for various stories.
There are many outlooks into who or what Kutulu is. Some think it is just a large serpent/squid in the ocean, others see it as a deity. I, personally, go with the deitistic view of it, comparing it to the Hebrew deity LVYThN(Leviathan), the Enochian deity, KRNZN(Choronzon), and the Lovecratian deity Nyarlathotep. The harnessor of the great will, the Mighty Living Continuum called Ab-Zu by the Sumerians. The force that wills it.