The Sumerian gods were traditionally tied to one or more cities in which their main temple stood. For example, Enlil was the city god of Nippur and Nanna that of Ur; Inana and An shared a temple in Uruk, and the sun god Utu’s main temples were in Sippar and Larsa. Each deity was associated with their own set of stories, symbols, rituals, and religious practices; and together they formed a loosely defined and constantly changing pantheon.
Over time, the Sumerian gods were merged with their Akkadian counterparts, much as the Roman gods were merged with the Greek. Nanna was equated with Sîn, Utu with Shamash, and so on. Some gods were also syncretized; for example, Ninurta and Ningirsu were originally separated deities, but by the beginning of the second millennium they had completely merged into one. Below, the Akkadian name (if different from the Sumerian) is given in brackets.
Depending on the political fortunes of the cities to which they were connected, the gods could rise or fall in status. For example, Ilaba, city god of Akkad, fell into total oblivion after the end of the Old Akkadian period, while by the end of the second millennium BCE, Marduk had eclipsed Enlil as ruler of the gods, due to the political ascendancy of his city Babylon.
The Adda Seal, showing the gods Ishtar, Ea, and Usimu. Wikimedia Commons.
An (Anu) was the god of heaven, the grandfather of the gods, and the city god of Uruk together with Inana. He is often depicted as an avuncular figure, with great moral authority but little direct power in the assembly of the gods.
Enlil was the city god of Nippur and the king of the gods. He is generally depicted as an irascible figure, who reacts strongly to perceived slights and often overreacts—most spectacularly so in the story of the Flood, where he decides to destroy all humankind because their noise is keeping him awake.
Nanna (Sîn) was the god of the Moon and the city god of Ur, where Enheduana served as high priestess. There are not many myths about Nanna, but those that do survive often connect him to cattle, due to the crescent-like shape of their horns. He is also known as Dilimbabbar (the name can also be read Ashimbabbar); and his spouse was the goddess Ningal.
Dumuzi (Tammuz) was the god of shepherds and the youthful lover of Inana, as recounted in a corpus of Sumerian love songs. The myth of Inana’s Descent tells of how Inana, in order to secure her release from the Netherworld, made Dumuzi take her place in the realm of the dead. He is also known as Ushumgal-An, “The Basilisk of Heaven.”
The Anuna (Anunnaki) and the Igigi were two groups of gods whose nature and relation changed over time. When Enheduana’s poems were composed, the Anuna were the higher gods and the Igigi the lower ones, but in later sources, the Igigi became the heavenly gods and the Anuna became the gods of the Netherworld.
Ishkur (Adad), the storm god, and Ashnan, the goddess of grain, appear in Enheduana’s poems as personifications of the storm and grain respectively. For example, when Inana’s roar is said to equal the storm, it is literally said to equal Ishkur’s; when grain disappears from the conquered mountain, it is literally Ashnan that disappears from it.
Enki (Ea) does not appear in either the Exaltation or the Hymn, but he is a central figure in Sumerian literature more broadly. He is a trickster god with a close connection to Inana, helping her out when she gets herself into trouble (Inana’s Descent) and bestowing upon the role of cosmic contrarian, charging her with introducing chaos into the cosmic order (Enki and the World Order).
Further reading
Ancient Mesopotamian Gods and Goddesses.
Enheduana 
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