This Semitic term describes a group of possibly seven or eight gods. It is likely that the god Marduk was one of them, but the total membership in this group is unclear and likely changed over time.
Like the term Anunna, the term Igigu is equally complicated and in need of a comprehensive new study. Igigu, which is likely of Semitic origin, indicates a group of gods in the Mesopotamian pantheon. It is, however, not entirely clear what distinguishes the Igigu from the Anunna.
The story of Atrahasis, the Babylonian story of the Flood and a precursor to the flood story in the Gilgameš Epic (Tablet XI), offers some evidence on the relationship between the Annunaki and the Igigu. The poem begins with the lines "When the gods like men bore the work and suffered the toil, the toil of the gods was great, the work was heavy, the distress was much" (lines 1-4) (Lambert and Millard 1999 : 43). The composition continues: "The Seven great Anunnaki were making the Igigu suffer the work" (lines 5-6) (Lambert and Millard 1969 : 43). What follows is partly fragmentary, but seems to indicate that the Igigu gods did not want to work any more and therefore the Anunnaki had to find a solution. Ultimately, this led to the creation of humans, who from then on had to bear the gods' work. In this story it appears that the Igigu were subordinate to the Anunnaki (von Soden 1989: 341-2). It is unclear which deities were included in the Igigu group.
In the prologue to the famous Code of Hammurabi it is indicated that the Anunnaki elevated the god Marduk among the Igigu gods (for a translation see Roth 1997: 76-142; also see von Soden 1966: 144), but it is difficult to assess the significance of this passage.
Some mythological texts, such as the Anzu myth, speak of an assembly of the Igigu gods, but whether this might be an institutionalized assembly, as suggested by Kienast 1965: 146, remains doubtful.
As mentioned above, it is not clear how many and which gods belonged to the Igigu, although the god Marduk appears to belong to this group for certain. It is possible that the group included only seven (von Soden 1966), eight (Kienast 1965: 144) or ten (Black and Green 1998: 106) gods, but this is uncertain as well.
Other gods who may belong to this group are Ištar, Asarluhi, Naramṣit, Ninurta, Nuska, and Šamaš (Kienast 1965: 149). Some gods seem to belong to both the Anunnaki and the Igigu (Kienast 1965: 152), yet more research is needed to gain a better understanding of this situation in the first millennium BCE.
We currently know of no cult places for the Igigu. Kienast (1965; 1976-80) has repeatedly suggested that the Igigu are only attested in literary and mythological texts. However, von Soden (1966) has brought forth some evidence that might indicate that there are very few theophoric personal names which invoke the Igigu, thus offering some evidence for their veneration.
The term Igigu is first attested in texts from the Old Babylonian period (Kienast 1976-80: 40; von Soden 1989: 340) and only occurs in Akkadian contexts (Edzard 1976-80: 37). A Sumerian logographic equivalent of the term Igigu is nun-gal-e-ne, to be translated as "the great princes/sovereigns." This term is mentioned in a literary text that has been ascribed to the princess Enheduanna, daughter of king Sargon, the founder of the Old Akkadian dynasty (Inana C, ETCSL 4.7.3 l. 2). This particular composition is only attested in Old Babylonian manuscripts and it is unclear whether an older date can be proven. According to Edzard (1976-80: 39) it is possible that nun-gal-e-ne was originally an epithet of the Anunna gods that later became identified with the Igigu under influence from Akkadian.
The Igigu and Anunnaki are frequently attested in literary, mythological, and religious (incantations and prayers) texts until the end of the cuneiform tradition. The Igigu are mentioned, among others, in the Anzu myth (Foster 2005: 555-578), in Enāma eliš (Foster 2005: 436-486), and the Erra poem (Foster 2005: 880-913), all of which are attested in manuscripts of the first millennium BCE.
Because this term describes a group of gods, there are no known images of the Igigu.
The etymology of this term is unclear. It has been suggested the term is of Old Akkadian (Kienast 1965: 157; 1976-80: 40) or of (Old) Amorite (von Soden 1966: 144) or possibly Arabic origins (von Soden 1989: 340). For the various spellings see Kienast 1965: 142.
Nicole Brisch, 'Igigi/Igigu (a group of gods)', Ancient Mesopotamian Gods and Goddesses, Oracc and the UK Higher Education Academy, 2012 [http://oracc.museum.upenn.edu/amgg/listofdeities/igigi/]