Coined in English 1387, the word "hero" comes from the Greek "heros", which originally translated as "protector" or "defender". What is a hero, though? What qualities define your character as actually being heroic?
Is your hero just holding the title by virtue of being the main character in the story? There are plenty of those out there and you may know a few. They lack strength of character, sense of responsibility, compassion for others...Well, you're smart enough to see where this is going. We're not talking about a heroic hero.
Maybe you're working with a tragic hero who has been set on his heroic path by tragic circumstances. You know, Superman and Batman sort of heroes who rise from being orphaned into perservering champions. Some are also obviously superhuman, though that isn't a prerequisite. In some cases, it adds to the story and in other cases it works better for the hero to be very human, putting life and limb at risk for the sake of others. Either way, it sounds like you're building a role model worthy of the title. This is why their level of sacrifice is important. Batman was orphaned when he watched the murder of his parents, setting down a purposeful path for his wealth and focus and sacrifices yet to come. Superman had a larger sacrifice up-front with the death of not only his parents but his entire world. Then, he had to learn how to live among the people of Earth with the unique hidden burden of ever-growing power.
You can have a reluctant hero or a brooding hero or one who eagerly embraces a destined path. In our modern age, an audience is also likely to encounter a rough-cut anti-hero who doesn't really care about others, but whose goals happen to coincide with some outcome that's good for somebody who isn't bad. Your hero may even be a vigilante, operating so far outside the law that "right" and "wrong" have new definitions. The recent film "Despicable Me" was as devoid of law and order as "A Fistful of Dollars", with both the protagonist and the antagonist operating as self-proclaimed villains dedicated to outperforming each other in magnitude of criminal grandeur. The protagonist only crossed the line at the story's climax when he set his own wishes aside in favor of...OK, again you're smart enough to see where we're going.
Just because your hero isn't a clean-cut milk-drinker who contributes to widows and orphans doesn't mean he has to turn in his badge. There are a lot of different kinds of heroes. Some of them wouldn't even get along with each other. Some use weapons and some are willing to kill to achieve their goals. Some justify their actions easily while others go through endless internal conflicts. They're all fine as long as they measure up to getting the part of their job done that dictates they put their own issues aside to fulfill their heroic purpose. What that purpose is...Well, we've established that you're supposed to be smart and it's your story, so you tell me. What is your hero doing to earn the title? What sacrifices and conflicts have challenged your hero to grow into the role?
What makes your favorite hero tough enough to have earned the status?