Someone asked me a while ago to write more for Asmodeus, but I don't have enough hc to fill an ask, so let me just put forward my theory about everyone's favorite pookie.
Hear me out, the core four (Satan, Mammon, Leviathan and Beelzebub) are all demons. Born a demon, stayed a demon, all good. Lucifer and Belphegor are fallen angels...
What if... what if they make Asmodeus the same way he is (sometimes) in demonology, so the son of Adam and Lilith. Idk how they'll explain that since Lilith isn't really a character in this game, but it would be so fun to see.
Maybe that's why he stays a lot in the human realm, because he feels a certain kinship with humanity that none of the other kings share. Maybe that's why he doesn't have kids with demons, because it would require giving his sperm to his mom and that'll be weird.
Anyways, even if you don't subscribe to Asmodeus is the son of Lilith and Adam theory, you have to at least acknowledge that him and Lilith have some sort of relationship. In mythos he's either her husband or her child. But I personally prefere the "Asmodeus is Adam and Lilith's child".
Would that make him the first devil? Like, of course, in terms of years, only God can beat Lucifer, but I'm talking as "was Asmodeus the first demotic creature?"
I don't really know, we have way too little knowledge of these characters to say what's 100% factual. But hey, that's just a theory, a 'I haven't slept in a week' theory!