My primary resource on these things, the Urban Dictionary, defines hero as “Someone who helps without anything expected in return. Their gesture may be big or small, profound or not, it doesn't make im' any less of a hero.”
In his speech in Tucson tonight President Obama said “We are grateful for Daniel Hernandez, a volunteer in Gabby's office who ran through the chaos to minister to his boss, tending to her wounds to keep her alive. We are grateful for the men who tackled the gunman as he stopped to reload. We are grateful for a petite 61 year-old, Patricia Maisch, who wrestled away the killer's ammunition, undoubtedly saving some lives.”
And so I give you a hero ….
Complete text of President Obama's speech.