Why is batman called the dark knight?

A Dark Knight is someone who doesnt care about being seen as a big hero, and doesnt care about being looked up to and loved, it is someone who doesnt really do the RIGHT thing, but the thing the must be done to keep poeples hope and faith.

like in the Dark Knight movie, at the end where Harvey (two face), kills all them people, even though thousands of civilians look up to him as a hero.

so Batman takes the blame for the killings at the end, he doesnt care about being looked up to, he takes the blame to keep the peoples faith in Harvey, so they wont know the terrible things he did.

this is what makes him a Dark Knight, he took the blame for someone elses mistakes, just so people dont loose hope in a great person who went bad.

hope you understand that!