From my particular perspective I believe "possession" is the religious mythical equivalent of the secular psychological phenomena of so-called Multiple Personality Disorder or paranoid schizophrenia. I am dubious as to the existence of either phenomena, spiritual or secular.
Even if the possessing "demon" doesn't use a conventional name like Frank or Carol or John or something, and uses a name that is "clearly" not a human kind of name, this makes no difference (after all how could we verify the authenticity of the name the "demon" gives us were we to perform an exorcism?). My hypothesis would be that the possessing personality aspect claiming a non-human pedigree is self deluded, playing games.
I'm not expressing myself well here... But do you read any Dean Koontz novels? He's a writer of psychological terror novels. There was one book he wrote called Hideaway. The protagonist, a human being despite his evil, had rather convinced himself that he was a spawn of Hell, that he had always been a demon-spawn in harmless human clothing his whole life -- he assigns himself this role retrospectively, you see.
So, this "demon" personality aspect could very well toss aside his "human" connection and take a new name for himself, (no offense here) but rather like nuns who go into the convent and priests who join the order, and take "new" names.....
As for prophesy, if you are referring to the Judeo-Christian tradition, prophets were really nothing more or less than political commentators and forecasters of their times.