Where did Demons, Angels, and "Unclean" Spirits originate from?

I've been studying a bunch of extinct religions lately. And I started getting sort-of interested in Ancient Mesopotamian Religions (i.e. Babylonian, Sumerian, etc...) and I was wondering where Demons and Angels originated from. I've read some Greek mythology about the Nature God Pan, and how the Biblical Satan was inspired by that Greek God. I've read about Pazuzu too, and how he was the "king of demons" in the Babylonian/Assyrian Religion. I was wondering if that's where demons had originated from: since it is Babylonian and the Bible does speak of Babylonia.

I know that the Bible and the Christian religion in general takes influence from several ancient religions. But I was wondering where the whole "unclean spirits" came from. Theologically speaking. -- I don't know much about where Angels originated from, just that there are 7 Archangels in the Catholic Religion (Uriel, Gabriel, Raphael, etc...). Did they come from any ancient religions? Or did they originate in Judeo-Christianity? - Thanks.

(I'm an Atheist, just curious about old time religions, and theological lore.)