Mordecai was a Jew living in Susa, the Persian capital.  He was a descendant of one of the exiles from Jerusalem.   He was also the guardian and adoptive father of his orphaned cousin Esther.  The long and the short of it is that, in the ensuing "Persian Idol" contest to replace Vashti, Esther beat out all the other contestants.  
    
          Esther won the favor of everyone who saw her....Now the king was attracted to Esther more than to any of the other women, and she won his favor and approval more than any of the other virgins. So he set a royal crown on her head and made her queen instead of Vashti (Est 2:15-17).

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           Xerxes then gave another banquet to celebrate Esther’s coronation.  Presumably, she did not refuse to grace his table.      

       

This process of preparation and selection is reminiscent of Daniel’s probation in the court of Nebuchadnezzar (Dan 1).  Like Esther, he found favor before the king and was promoted.  However, Mordecai told Esther not to tell anyone she was a Jew (Est 2:20).  That he felt it necessary to hide this fact shows us that the exiles were experiencing some degree of racial discrimination in their temporary home.