User blog comment:B214/DxD Zero: Sirzechs story/@comment-2003:45:5D00:9D00:D59D:7785:ABEF:4D2C-20181006195431/@comment-37165251-20181011200320

That´s the Question.

I think that Lucifer and the Fallen that rebels with him against God became the First Devil through a Ritual and after that he created the Rest with Lilith´s help.

But it is only my Theory