Esther is the heroine, the main character. That's obvious, given that the book is named after her (though she gets about the same amount of stage time as some of the other major characters like Ahasuerus, Haman, and Mordecai). But Esther isn't naturally heroic. She has to get spurred into it by her legal guardian (as in "parent or legal guardian"), Mordecai.
When she first receives Mordecai's plea for her to help save the Jews from Haman's plot, she tries to find a way out of it. She tells Mordecai: "All the king's servants and the people of the king's provinces know that if any man or woman goes to the king inside the inner court without being called, there is but one law—all alike are to be put to death. Only if the king holds out the golden scepter to someone, may that person live. I myself have not been called to come in to the king for thirty days" (4:11).
But after a fairly harsh warning from Mordecai, she decides to help anyway. So, she isn't initially willing, which is often the case for heroes in stories. Luke Skywalker doesn't kick into hero mode until the Empire's Storm Troopers kill his aunt and uncle (to give another example). There needs to be a catalyst. For Esther, Mordecai's weeping and wailing and sack-cloth wearing and cajoling provide that.
Also, Esther is pretty different from the other most prominent female character in the story, Vashti (the former queen). Vashti wouldn't put up with the king's foolishness and his attempts to show her off as an object to his nobles. But Esther takes a different approach to Ahasuerus. She's nobody's fool, but she's willing to work to rise up through the harem, currying favor with the eunuchs in order to become queen. Then, she uses her position of power to please the king in order to get the kind of outcome she desires. Esther puts up with the king, but she gently and somewhat slyly manipulates him to her advantage.
Some have argued, though, that Esther isn't exactly a role model. Peace isn't exactly restored after Haman gets killed and his plot is canceled. On the contrary, massive retaliatory vengeance ensues, with thousands of Haman's supporters slaughtered in the Persian capital and in the provinces (75,000 people in all are killed, according to the book). And Esther seems to be pretty cool with this. By modern standards, mass-murdering vengeance for a mass-murder that didn't actually take place might seem more than a little extreme or morally questionable.
This massacre is about revenge, though, not profit, as the book makes clear (unlike Haman's attempt at genocide, which was about both). The book has a very "eye for an eye" sort of moral (though, since Haman's massacre didn't happen, only one side actually loses an eye). At any rate, the character of Esther seems both modern and ancient—subtle and cautious in her attempts to gain power and solve problems, somewhat unyielding and harsh in handing out beat-downs.
Also, as for the origin of Esther's name, it's not Hebrew—her Hebrew name is actually "Hadassah," which means "Myrtle." The name Esther might mean, "Star," or it could also be a reference to the Babylonian goddess "Ishtar" (since the Jews in exile received Babylonian names).