As with most of the OT writings the author of the book of Esther (Esther meaning “star”) is not mentioned. The Jewish historian Josephus names Mordecai as author of the book. Chapter 10:2-3 however speaks against this, for the author would hardly have written likewise of himself. On the other hand chap. 9:20 explicitly mentions that Mordecai wrote these things. Other sources ascribe the book of Esther to Ezra or Nehemiah.
In any case the author was a Jew whose heart was set on the fate of the people of Israel. Besides he had an excellent knowledge on the situation at the Persian court. This very fact was fully acknowledged by the Greek historian Herodotus and by the excavations of the past hundred years.
The events of the book of Esther occurred during the reign of King Ahasuerus, Xerxes I. (Persian: Khschayarscha).
Ahasuerus reigned from 485 to 464 BC. His predecessor was King Darius (522-485 BC) who is mentioned in Ezra 4:5. His successor was Artaxerxes I. (Ezra 7:1 and Nehemiah 2:1). The events mentioned in Esther therefore happened between Ezra chapter 6 and chapter 7. This is why many presume that the book was written in the second half of the fifth century BC.
This book particularly teaches us the invisible care of God for those of His people who preferred to stay in the land of exile although they could have returned to Palestine since the days of King Cyrus of Persia (see book of Ezra). Jehovah watched with tender goodness and care over this large part of the Jews, which He could no longer recognize as His people in front of the world. He hid Himself before them as it were. This is why God is not mentioned once in this book. Already in the antiquity the Jews had considered this striking characteristic as fulfilment of the prophecy in Deuteronomy 31:18.