What does “He is the Ahasuerus” mean?

Question

Why in the first pasuk of Megillas Esther is it written that Ahasuerus is the Ahasuerus that ruled from India to kush? Where there other Ahasuerus's that were important enough that in our bible we wrote "that the Ahasuerus is the Ahasuerus..."

One answer that I though about was that it is like saying Henry the 5th, but in our Torah we try not to add more words if we can avoid it. Since in our generation we do not know the other Ahasuerus's this part of the pasuk looks redundant the pasuk could of bean written as:

"וַיְהִי, בִּימֵי אֲחַשְׁוֵרוֹשׁ: הַמֹּלֵךְ מֵהֹדּוּ וְעַד-כּוּשׁ--שֶׁבַע וְעֶשְׂרִים וּמֵאָה, מְדִינָה"

Answer 1

The Gemara in Megillah 11a expounds the repetitive nature of this statement as meaning

הוא אחשורוש הוא ברשעו מתחילתו ועד סופו

“This is [hu] Ahasuerus” (Esther 1:1); the term hu, this is, comes to teach that he remained as he was in his wickedness from beginning to end.

I.e. he was the same old evil person from the beginning to the end.

Answer 2

Rashi

Rashi on Esther

It was in the days of Achashveirosh. He was the king of Persia. The Persians conquered the Babylonians, and Achashveirosh succeeded Koresh to the Persian throne in the year 3392. who reigned in place of Koresh There were other Persian kings with the name “Achashveirosh,” therefore Rashi identifies which “Achashveirosh” he was. (Mizrachi) at the end of the seventy years of the Babylonian exile.