Who is Mordecai in Bible?

The king was sending his orders to each nation in their language. This means that at least one person was Jewish who knew to write in Hebrew.

Only one person did not bow to Haman and that person, Mordecai, claim that this is because he was Jewish. It is clear that there was no other known Jewish that did bow.

So Mordecai was the Jewish representative in the King's court that represent his Jewish nation and translated the King's orders to the Jews.