Little can be said about the anonymous author of Esther. He is not named in the text of Esther and there is no information about him in it either. The medieval scholar Ibn Ezra (1089-1167) attributed the book to Mordecai, as Clement of Alexandria had done earlier, while Augustine thought of Ezra as a possible author. Jewish tradition (the Baba Bathra 15a) mentions the men of the Great Synagogue
as the authors of Esther. All that is clear to us is that the author had a proper knowledge of Persian life, customs, names and expressions, on the basis of which it is highly probable that the author was a Persian Jew.1
1 Now in the days of Ahasuerus, the Ahasuerus who reigned from India to Ethiopia over 127 provinces,