It is, in all honesty, the most over used in the English Language.
Sir Edmund Hillary - the first man to scale Everest - died yesturday morning at age 88. While listening to the Radio this morning, people phoning in proclaiming he was "a true hero".
He isn't.
His feat was astounding, many people had (and have since) attempted it, and where some have succeeded, some have also died. I'm not trying to take this achievement away from him, but scaling the tallest mountain in the world makes you an amazing mountaineer, not "a hero".
It's the same in other places too.