Why does Esther change her name?

Esther is initially called Hadassah (Esther 2:7). Why does she change her name, ostensibly even before she is brought to the king's harem?

Answer

Haddasah was her hebrew name she changed her name to Esther which is Persian, as is Mordechai, to either hide her Jewish identity or, more likely since the megillah was written by her and Mordechai, to show that she has a sense of nationalism.