First some explanation of the titles or groups whom the Gods of Mesopotamia belonged to :
Sumerian Anunnaki, Acadian Anunna
It is a loan word (plural only) from Sumerian a.nun.(n)a(k) ‘semen/descendants’ of the (-ak) monarch (nun) and refers to the offspring of the King of Heaven An. The gods together are called Anunnaki and in the text one might specifically add Anunnaki s-a-s-amê u er Setim, ‘the Anunnaki of heaven and earth’.
The definition of the term Anunnaki is the “children of An and Ki”.
Anunnaki is thus a collective name for the gods of Heaven and Earth of which the “triad” of Gods belonged to. The most important Gods of the Mesopotamian pantheon were : Anu, Enlil and Enki, earliest headed by An and later by Enlil.
In Mesopotamian cosmology, heaven, where the gods ‘play’. The Anunnaki and Igigi met in heaven in Ubshu-ukkinakku, the divine assembly hall.
The Gilgamesh Epic has the gods dwelling in the cedar mountain. They had their parakku, throne-bases, there. It was an enormous tree at the cedar forest and was guarded by Humbaba.
There is a stairway up to heaven from the “underworld” called Kur (another name for Africa). An as King of the Anunnaki and Igigi. The Sumerians had further four leading deities, known as creating gods. They were the leaders of the Anunnaki and Igigi :
Anu, the god of heaven
Ki (Kiki), the goddess of earth
Enlil, the god of air
Enki (who later became Ea by the Babylonians), the god of water
At the next level were fifty “great gods”, they also belonged to the Anunnaki, although several gods confined to the “underworld” are specifically designated Sebitti.
2. Igigi and Sebitti
The Igigi are the Gods of the Younger generation. They were given the task of digging gold and riverbeds by the Anunnaki.
After a long period the Igigi tired of this unpleasant work, revolted, and forced the Nibiruan leaders (the “triad” of Gods) to find a “new” source of labor.
Their solution, related in great detail in the Sumerian records, was to create a slave race by splicing their genes with the genes of the most advanced primate on the planet at that time, probably Homo Habilis (approximately 440,000 years ago).
Thus was born humanity, first Homo Erectus, Neanderthaler and Cro-Magnon man, not Mankind. Mankind was created much later as we will see.
The Sebitti are the seven warrior gods led by Nergal (Erra) also called the Underworld Gods. In the sky they are the Pleadies. They are the children of Anu and the Earth-mother.
In the Book of Enoch they were called “The Watchers” and in the Bible Nephilim.
3. Demi-Gods, Demons and Monsters
Demi Gods and Demons, the children and Creations of the Anunnaki, they were worshipped as Gods too
In the Sumerian cosmology there was, first of all, the primeval sea (Abzu), from which was born the cosmic mountain consisting of heaven, ‘An’, and earth, ‘Ki’.
In the Bible they are called Anakim, Anak, Anakites, Arba and Rephaites. This is what in the bible is written about the Anakim:
Dt:1:28: Whither shall we go up? our brethren have discouraged our heart, saying, The people is greater and taller than we; the cities are great and walled up to heaven; and moreover we have seen the sons of the Anakims there.
Dt:2:10: The Emims dwelt therein in times past, a people great, and many, and tall, as the Anakims;
Dt:2:11: Which also were accounted giants, as the Anakims; but the Moabites called them Emims.
Dt:2:21: A people great, and many, and tall, as the Anakims; but the Lord destroyed them before them; and they succeeded them, and dwelt in their stead:
Dt:9:2: A people great and tall, the children of the Anakims, whom thou knowest, and of whom thou hast heard say, Who can stand before the children of Anak!
Jos:11:21: And at that time came Joshua, and cut off the Anakims from the mountains, from Hebron, from Debir, from Anab, and from all the mountains of Judah, and from all the mountains of Israel: Joshua destroyed them utterly with their cities.
Jos:11:22: There was none of the Anakims left in the land of the children of Israel: only in Gaza, in Gath, and in Ashdod, there remained.
Jos:14:12: Now therefore give me this mountain, whereof the Lord spake in that day; for thou heardest in that day how the Anakims were there, and that the cities were great and fenced: if so be the Lord will be with me, then I shall be able to drive them out, as the Lord said.
Jos:14:15: And the name of Hebron before was Kirjatharba; which Arba was a great man among the Anakims. And the land had rest from war.
Gn:10:6: And the sons of Ham; Cush, and Mizraim, and Phut, and Canaan.
Gn:10:7: And the sons of Cush; Seba, and Havilah, and Sabtah, and Raamah, and Sabtechah: and the sons of Raamah; Sheba, and Dedan.
Gn:10:8: And Cush begat Nimrod: he began to be a mighty one in the earth.
Gn:10:9: He was a mighty hunter before the Lord: wherefore it is said, Even as Nimrod the mighty hunter before the Lord.
Gn:10:10: And the beginning of his kingdom was Babel, and Erech, and Accad, and Calneh, in the land of Shinar.
Gn:10:11:Out of that land went forth Asshur, and builded Nineveh, and the city Rehoboth, and Calah,
Gn:10:12:And Resen between Nineveh and Calah: the same is a great city.
Chronology of the Mesopotamian Gods
It is notable that some of the Gods don’t have a counterpart in the Sumerian and also some of them in the Acadian religion and on the other hand some of their Gods are unknown in Babylonian religion.
For instance : Tiamat, Lahmu and Lahamu and some others, are only known in the Babylonian religion.
In my opinion is that a normal phenomenon because the Sumerian and more or less also the Acadian religion are much older than the religion of the Babylonians (most of the religion of the Babylonians was taken over from the Sumerians and Acadians). Consider also that the Babylonian religion later on was taken over by the Jews and afterwards also by Christianity and the Moslems.
The root of all Semitic nations and their languages are also from Sumerian origin. In my opinion is the Sumerian religion the most “pure” story about our ancient history and the beginning of religion, together with the religion of India and the Aryans.
Tiamat, Lahmu and Lahamu for instance can be seen as Heaven and Earth at the beginning of time. They were later worshipped as Gods by the Babylonians, even in the Sumerian religion are some Gods identified as the planets.
The Babylonian God Marduk (the highest God of Babylon) has in my opinion his counterpart in the Sumerian God Enki. (the Father and the Son doctrine, also known by the Jews and Christianity).
Most scholars have another meaning about the origin of some Gods, as specially:
An and Anshar can be different Gods
Ki and Kishar can also be different Gods
An and Anu are both one and the same God
When you read the story of An and Anu carefully there is only one possibility:
The name Anu is used from about 2,000 BCE, the beginning of the Babylonian period, and they mixed the Sumerian Gods An and Anu and called him Anu and made An and Anu one God.
An and Anu were different Gods.
In accordance to the theory of Emanuel Velikovsky, in his book “Oedipus and Echnaton” JUPITER was the same as the God:
AMON in Egypt
MARDUK in Babylonia
ZEUS in Greece
MAZDA in Persia
SIWA in India
Source: http://www.bibliotecapleyades.net/sumer_anunnaki/esp_sumer_annunaki12a.htm#Gods of Heaven and Earth