Who is Our Father Below (the Devil) from The Screwtape Letters and what is their importance?

A self-worshipper, the Devil is not clearly delineated as a character. Unable to understand love, unable to understand the Creator's love for the human creatures, assertive of his own position and pre-eminence, we can only imagine the Devil to be Screwtape taken to the furthest possible extreme. His character is perhaps best depicted when it is said he wishes to own everything in the universe on the basis of conquest and that he is a worshipper of himself.