Who is the "reaper" in the song "Don't Fear the Reaper" by Blue Oyster Cult?

I heard the song on a show I was watching the other night. It sounded like this, http://www.youtube.com/watch?v=z5rW-YvYmUE. That's obviously the link... I was curious to who the reaper was. It's a very good song by the way, hard to sing though.