After reading this question - I am now more confused!
The Gemara in Rosh Hashanah 3b writes that Cyrus, Darius and Artaxerxes were all the same person:
All three names are referring to the same person: He is Cyrus; he is Darius; and he is also Artaxerxes. He was called Cyrus [Koresh] because he was a virtuous [kasher] king; he was called Artaxerxes after his kingdom, i.e., this was his royal title; and what was his real name? Darius was his name. (Sefaria Transaltion & Notation)
Cyrus is largely praised as being a righteous king (as stated above that he was named Cyrus because he was 'kasher' king). Indeed we know that he gave permission for the Temple to be rebuilt (See Ezra 6:3) and then we see in Seder Eliyahu Rabbah 19 that he wept over the Temple's destruction.
The continuation of the above cited Gemarah says that he became corrupt. So something happened that made him turn and it would seem that he went from one extreme to another.
Esther Rabbah 1:3 tells us that Artaxerxes was in fact Achashveirosh! and He was called Artaxerxes as he would flit between seething with rage and then relative calm. There are several sources that point to the fact that Achashveirosh was real 'rashah' (wicked man). In Esther Rabbah 7:20 we're told that he hated the Jews more than Haman! And the Gemarah (Megillah 12a) tells us that he had no problem wearing the priestly vestments.
So my question is two-fold:
- What happened to make him switch from being a friend of the Jews to such a virulent hater?
- And do we know a timeline as to when this all played out?