He's the old Jewish guy in the book of Esther. We first meet Mordecai in Esther 2:5-7.
"Now there was in the citadel of Susa a Jew of the tribe of Benjamin, named Mordecai...[who] had a cousin named Hadassah, whom he had brought up because she had neither father nor mother. This girl, who was also known as Esther, was lovely in form and feature, and Mordecai had taken her as his own daughter when her father and mother died."
If you know the story of Esther, then you know that King Xerxes chose her as his new queen. Apparently he didn't ask her nationality because no one was aware that Esther was Jewish. Fatherly Mordecai advised her to keep that information to herself, no doubt to protect her. The text doesn't say he told her to lie, so we can assume that no one bothered to inquire about it.
Well, one day while Mordecai is sitting outside the king's gate, he overhears a plot against the king's life. He tells Esther who tells the king and the would-be assassins are hung. Score for Mordecai!
One day King Xerxes honors a dude name Haman. Haman gets the big head and everyone is to bow down or kneel when he goes by. My man Mordecai wouldn't do it. The text doesn't tell us why he wouldn't, but my guess is he could easily see that Haman was full of himself and didn't deserve that kind of honor. He also may have felt that only the king and God himself deserves that kind of respect. I don't know, but part of me wants to give Mordecai a high-five for standing up for his beliefs even though it clearly went against the king's orders. Sometimes ya just gotta do what is right no matter what!
I'm sure we can all imagine how Haman reacted. But Haman was crafty. He knew Mordecai was a Jew and he apparently didn't like any Jews, so he devised a plan to get rid of them all, not just Mordecai. His plan, however, backfires when good ol' Mordecai learns of it and tells Esther. Esther lives out the famous verse in chapter 4, verse 14, "...for such a time as this" and saves her people. In the process, Haman's ugly heart is revealed and he is hung on the very gallows he built for Mordecai. Score again for Mordecai!
So why is Mordecai, some obscure Jew in the Old Testament, my hero? Because...
He did what is right.
He didn't back down.
He didn't brown-nose (I hate that term but sometimes is just fits!).
He saw something bigger than himself.
He went from being an old man sitting at the king's gate hoping to catch a glimpse of his beloved daughter to having his "greatness" proclaimed throughout the entire land in chapter 10.
All because he did what is right and good.
If that ain't a real hero, then I don't know what is.