Ishtar was the consort of Marduk and a Sun Goddess. Her following diminished in Babylon during a patriarchal shift in society. The book of Esther in the Bible is believed by some to be in deference to the steadfastness of Ishtar's followers, in that a resurgence of the Goddess cult rendered the nation of Babylon more peaceful and non-combatant, resulting in the release of Israel.
I had heard, but have not verified, that the Book of Esther is the only book of the Bible in which the name of God is not spoken. If this assertion is correct, the assumptionthat the ancient Hebrew scholars took Ishtar as their own and Esther resulted is more sanguent.