Inanna was worshipped in Sumer at least as early as the Uruk period (c. 4000 BC – c. 3100 BC), but she had little cult prior to the conquest of Sargon of Akkad. During the post-Sargonic era, she became one of the most widely venerated deities in the Sumerian pantheon, with temples across Mesopotamia. The cult of Inanna-Ishtar, which may have been associated with a variety of sexual rites, including homosexualtransvestite priests and sacred prostitution, was continued by the East Semitic-speaking people who succeeded the Sumerians in the region. She was especially beloved by the Assyrians, who elevated her to become the highest deity in their pantheon, ranking above their own national godAshur. Inanna-Ishtar is alluded to in the Hebrew Bible and she greatly influenced the Phoenician goddess Astarte, who later influenced the development of the Greek goddess Aphrodite. Her cult continued to flourish until its gradual decline between the first and sixth centuries AD in the wake of Christianity, though it survived in parts of Upper Mesopotamia as late as the eighteenth century.
Inanna appears in more myths than any other Sumerian deity. Many of her myths involve her taking over the domains of other deities. She was believed to have stolen the mes, which represented all positive and negative aspects of civilization, from Enki, the god of wisdom. She was also believed to have taken over the Eanna temple from An, the god of the sky. Alongside her twin brother Utu (later known as Shamash), Inanna was the enforcer of divine justice; she destroyed Mount Ebih for having challenged her authority, unleashed her fury upon the gardener Shukaletuda after he raped her in her sleep, and tracked down the bandit woman Bilulu and killed her in divine retribution for having murdered Dumuzid. In the standard Akkadian version of the Epic of Gilgamesh, Ishtar is portrayed as a spoiled and hot-headed femme fatale who demands Gilgamesh become her consort. When he refuses, she unleashes the Bull of Heaven, resulting in the death of Enkidu and Gilgamesh's subsequent grapple with his mortality.
Inanna-Ishtar's most famous myth is the story of her descent into and return from Kur, the ancient Sumerian Underworld, a myth in which she attempts to conquer the domain of her older sister Ereshkigal, the queen of the Underworld, but is instead deemed guilty of hubris by the seven judges of the Underworld and struck dead. Three days later, Ninshubur pleads with all the gods to bring Inanna back, but all of them refuse her except Enki, who sends two sexless beings to rescue Inanna. They escort Inanna out of the Underworld, but the galla, the guardians of the Underworld, drag her husband Dumuzid down to the Underworld as her replacement. Dumuzid is eventually permitted to return to heaven for half the year while his sister Geshtinanna remains in the Underworld for the other half, resulting in the cycle of the seasons.
Inanna and Ishtar were originally separate, unrelated deities, but they were equated with each other during the reign of Sargon of Akkad and came to be regarded as effectively the same goddess under two different names. Inanna's name may derive from the Sumerian phrase nin-an-ak, meaning "Lady of Heaven", but the cuneiform sign for Inanna (𒈹) is not a ligature of the signs lady (Sumerian: nin; Cuneiform: 𒊩𒌆 SAL.TUG2) and sky (Sumerian: an; Cuneiform: 𒀭 AN). These difficulties led some early Assyriologists to suggest that Inanna may have originally been a Proto-Euphratean goddess, possibly related to the Hurrian mother goddess Hannahannah, who was only later accepted into the Sumerian pantheon. This idea was supported by Inanna's youthfulness, and as well as the fact that, unlike the other Sumerian divinities, she seems to have initially lacked a distinct sphere of responsibilities. The view that there was a Proto-Euphratean substrate language in Southern Iraq before Sumerian is not widely accepted by modern Assyriologists.
The name Ishtar occurs as an element in personal names from both the pre-Sargonic and post-Sargonic eras in Akkad, Assyria, and Babylonia. It is of Semitic derivation and is probably etymologically related to the name of the West Semitic god Attar, who is mentioned in later inscriptions from Ugarit and southern Arabia. The morning star may have been conceived as a male deity who presided over the arts of war and the evening star may have been conceived as a female deity who presided over the arts of love. Among the Akkadians, Assyrians, and Babylonians, the name of the male god eventually supplanted the name of his female counterpart, but, due to extensive syncretism with Inanna, the deity remained as female, despite the fact that her name was in the masculine form.