And another brief post:

The satan, it seems, is a nonhuman being, a type of angel, perhaps in some accounts an ex-angel or fallen angel, and he or it (somehow feminists never campaign that the satan should be referred to as 'she') comes to be opposed to humankind, and then to Israel, and hence, not surprisingly, to Jesus.

From Evil and the Justice of God, chapter 4 (pg 108 of the hardcover edition), by N T Wright.