As you know, I’m interested in TF (theo-fiction), stories like C.S. Lewis’ The Great Divorce that take the angels and devils of the old folk tales as their properties just as fantasy takes the fairies and dwarfs. First Things has just put up a a very interesting TF discussion about devils in fiction.
The linked piece specifically discusses the problem of making the devil a readable character without making him attractively Promethean like Milton’s Satan is said to be or attractively urbane and cosmopolitan like Mephistopheles. The author eventually concludes that writers should portray the devil as “a merciless real estate developer whose largest projects are all casinos,” or, in other words, as a lightly disguised Donald Trump.
I agree with some of the responses in the comments that C.S. Lewis succeeded in portraying the devil well but unattractively in Perelandra and in That Hideous Strength. That devil is powerful and malicious and childish, even idiotic in the technical sense. (The devil of the Screwtape Letters is equally well-done, but very different).
My current conception of devils as a characters in fiction owes something to Lewis but probably more to the Gospels. In the Gospels, devils possess people and make them go mad. We understand the possession, since we understand that flesh is a blessing and lack of flesh the curse God put on the satanic hosts when He cast them out. Naturally the devils want to taste the blessing and defy God. But why madness? To the extent we Mormons think about it at all, we portray the madness as a kind of maliciousness. The devils hate the people whose bodies they possess so they torment their minds and force them to abuse their flesh. Plausible enough, really. But its even more plausible to me that the devils are themselves insane. Of course modern prophets consistently warn us that Devil and his angels are clever and patient in their temptation. But the mad can be cunning and determined, while still being mad.
No real portrayal of the devil as a character emerges from Mormon scripture. This is a good thing. Curiousity about the personality of the devil is about the last thing scripture should encourage. However, the story of the pre-mortal counsel probably shows a character trait of a desire to control, while at the same time showing that he is cowardly (the devil and his angels were unwilling to risk a mortality where they could fail). Coupled with his traits in the Temple story, including petty delusions of grandeur, vindictiveness, and considerable self-satisfaction, Mormonism actually has a pretty complex picture of the devil.