Man, this books is weird, but great. The hook is the fantastical idea that a scientist creates a self-aware computer that claims to be- and may or may not actually be- Satan. The real meat of the narrative, though, is following the incredibly unfortunate life of Sy Kassler, a psychiatrist, as basically the universe turns against him in everything despite his usually good intentions and general competence. His life is just a train wreck for the most part, mostly through no fault of his own, and you can't help but feel awful for the guy throughout, while also being amused at the generally black comedic and deeply cynical tone of the whole thing. Partway through the book's timeline Kassler encounters and is hired to give therapy to "Satan" and in between the main narrative covering the general course of his life the book is intercut with their sessions, which are interesting yet ambiguous. A great cast of characters, some more sympathetic than others but all with a decent amount of depth. The books covers themes surrounding the nature of psychology and artificial intelligence, the general good-naturedness of people (or lack thereof) and of course the obvious religious themes.

I was lucky enough to find this in my dad's old collection as it's been out of print for ages. I highly recommend trying to track down a copy if you can. It was really something I'm not going to forget anytime soon.