User blog comment:B214/Volume 22 spoilers/@comment-201.215.165.7-20170213165134/@comment-26709288-20170215235220

"Ishibumi mostly sticks close to the origin stories, so really Lucifer in this case is a being who became the first devil because fiction since ishibumi is sticking close to myths origin. We won't get any information on him at all so this just holds to be more likely."

Not really, I mean Samuel was the one who tricked Adam and Eve when this role should've fell to Lucifer. And God didn't just make him a fallen angel, he made him a fallen angel-dragon hybrid. Inshubi changes alot of mythology for the plot. That's what makes DxD so interesting.

You also got to consider the possibiltiy that maybe Devils were their own race to begin with. Maybe God had nothing to do with devils, maybe they were always just their own race who opposed God and wanted the Earth for themselves. Maybe when the Original Lucifer turned Lilith into a devil, this is what sparked the Great War between the two. Unless he decides to finally explain it, we can't completely know for sure, we can only speculate.