[Conjecture]
I think that's Thanatos. Greek god, possibly of death, in psychological terms the classification for natural self-destructive tendencies, a proclivity to engage in harmful, risky past-times and the temptation to take the more dangerous course. It's why you can't help but poke a wobbly tooth with your tongue, why you get that strange urge to throw yourself off high places, why people have (as previously mentioned) fantasies about suicide, and some psychologists believe it's a big contributor to the allure of drugs, both legal and illegal. There's a corresponding term, Eros I think, that could just be related without being a counterpart.
[/conjecture]
Edit: Seems I've got Wikipedia on my side, a trusty comrade in the gloomy realms of approximate debate. They also named a euthanasia machine after the concept, and Thanatos wasn't a god, he was a Daemon (note apocalyptic "daemon" spelling, so much more infernal than the lesser "demon")
Maybe the author was trying to indicate the original meaning, the one it had before Christianity messed with it. There was nothing infernal about demons originally - they were guiding spirits, demigods, that sort of thing.
Ah, here we go:
http://www.etymonline.com/index.php?term=demon


