Efreet

I really like the idea of having mysteries in a game, so It would be nice to have a god that the player has to work to discover. Something like Vecna from D&D. The player would have to read books and search for clues about the god, and eventually find some lost temple. Ideally, the game wouldn't hold the player's hand in finding this deity, and there would still be some unanswered questions about his/her motives and practices in the end.