The Archangel Gabriel in History and Tradition, by Roxana Eliana Avashi

There's no origin story or anything for the es. Though, if you want to get into stuff outside the biblical canon about where the angels come from and all that, you get em into some wild and awesome territory. They are already part of our supernatural understanding of everyday reality in the world. As the monotheistic god is ultimately faithless, or at least does not reveal its face to humans. So for a god of gods to do human like things, it has to send a human like messenger.