Yeah, I love the mystery of He Who Was; to me, Asmodeus's betrayal dosen't seem to be simple case of Good vs. Evil because this god is defintely hard to pin down. I mean, he was probably better than his successor and his domain has been described as a "heaven", but I don't see him as necessarily a force for good, especially since he employed angels like Asmodeus and Alloces in the first place, neither of whom struck me as exemplars of goodness (to put it mildly) in their limited pre-diabolic depictions.
Yep, this is exactly the sort of reason why I'd prefer not to delve into the answers too soon. I love the JudeoChristian echoes, but I don't want this to be a
direct metaphor, and I like the idea that Asmodeus's predecessor wasn't necessarily a god of rainbows, light, marshmallows, and puppies.
Actually, while I would never do this as part of
official D&D canon, I love the idea of running a personal campaign in which it turns out that Asmodeus is actually the good guy--in which the god he overthrew was a being of hideous evil, and that he's set up the Hells to trap the souls of the damned as a
prison for evil beings, rather than as a means of increasing the power of evil in the cosmos.
(Again, not suggesting that for the real/official story in any way; in D&D proper, Asmodeus is a major bad guy, and he needs to stay that way. But it's an example of the kind of thing that you can do in your home game, aided by the fact that nobody knows exactly what He Who Was... was.)
