If there isn't a sequel to this game.. at least let there be something to tell us who the Outsider really is! How did he get to where he is now? Why choose Corvo, Emily, Daud, etc?
The source of all magic in the world, e.i. God and the Void is "the end of all things and the beginning".
He created it.
Because they have the potential to alter the course of certain events.
My theory on it is that The Outsider is the 21st century programmer who created the world and everything and everyone in it.
Everything except the matrix architect reference.