Hmm, that is a good question, certainly good recent biblical exegisis (spelling) would suggest that Satan as a singular being does not exist so much as "the Satan" being a role which was played by different people, or cosmic characters, at different times. There's a good chance that Jesus and his immediate followers were influenced by non-canonical Jewish books such as the book of Enoch, which deals with renegade angels, giants, the nephilem, demons etc.
There are versions of the scriptures which suggest that a resurrected Jesus told his followers either not to worry about Satan any longer or that Satan had been dealt with but that other horrors could be expected before the end of time.
Personally one of the greatest stories to feature Satan, based upon, mainly, Kabbalistic Jewish ideas but also Christian ones is Philip K Dick's The Divine Invasion, it explains quite brilliantly how the trauma of the incarnation of Jesus and the crucifixion could have effected a deity which was sharing in the experience, including the mind and thinking processes, of its creation, it explains psychological splitting, loss of memory, recover of memory etc. as possibly afflicting the deity and therefore the whole of reality. It also has one of the best depictions of Satan I've ever read as a kind of malignant donkey or goat creature. The ultimate prevailing of good over evil is done exceptionally well too.
I tend to think that some sorts of fiction serve God's purposes without being known about.
