An hero? Why is it an hero instead of a hero? An hero in not grammatically correct.

I've done at least four in a row with you present death.
Where's my props.
<grr>
WHO IS THIS MAN NAMED CRPYTEX???
surely everyone knows i am the master of knife kills.
i challenge you to a duel!!!
I accept! Name the time and place good sir!
An hero? Why is it an hero instead of a hero? An hero in not grammatically correct.
