"In discussing the story of “Inanna’s Decent to the Netherworld,” Diane Wolkstein comments on the interrelation between Inanna and her sister Ereshkigal, Queen of the Netherworld:
"In many ways, Ereshkigal is the other, neglected side of Inanna. Therefore, when she hears of the appearance at her gates of the “all-white” fertile, bedecked Goddess of Love, she is enraged, for Inanna’s light, glory and perpetual movement have, to some extent, been achieved at her expense. (158)
Ereshkigal, the neglected side of Inanna, has certain qualities that are similar to Lilith’s. Both are connected to nighttime aspects of the feminine—the powerful, raging sexuality and the deep wounds accumulated from life’s rejection—which seeks solace in physical union only…. The powerful Lilith of Inanna’s adolescent days had to be sent away so Inanna’s life-exploring talents could be developed. But now that Inannna has become queen of her city, wife to her beloved, mother to her children, she is more able to face what se has neglected and feared: the instinctual, wounded, frightened parts of herself. She now hears, and is capable of respond to, the labor of Ershkigal in the Great Below. (160)"
So Ereshkigal and Inanna are doppelgangers and alter egos—sharing many characteristics, but unable to be in the same place. This relationship is extended to Ishtar through the synchronizing of the Inanna and Ishtar."
Also, in some variations of the myth, Inanna’s descent into the underworld happens because she's summoned by a "consortium of underworld gods called the Anunnaki(meaning a "host of demons"), who were associated with magic and sorcery"
