What is a hero?

Is it a person living a heroic life?
Is it a person doing one heroic act?
What is that person gets paid to do heroic acts ie fireman, soldier etc?
I can't stop thinking about the Saint of Cabrini Green. Years ago I read about this man who in an attempt to stem gang violence in Cabrini Green waded into the middle of a gun battle between rival gangs to get them to stop. He literally walked into a hail of gunfire to get them to stop shooting. I don't know whats become of this man but thats a hero to me.

What's a hero to you?