Since @drconstellation is mocking my possible assumption about demon!Metatron, I purpose to stop, take a sip of cocoa and think.
WHO THE FUCK IS METATRON?
Neil said that he "wasn't ever a human" in the GOverse. Okay.
The Metatron is at the top, but he wouldn't actually show up on an organisational chart. He's just above everyone, and below God.
Not a word about his being an angel by nature.
And while I admit theoretically that cute bearded old man in final fiftheen MIGHT be a demon, I dont believe it seriously and i dont believe that Metatron has always been a demon. Just someone above everyone and below God.
Well, what we know about M:
He is kinda missing in employee database.
He is definitely not a human.
He never appeared in the office not as floating head.
Aziraphale calls him in s1 via the special divine communication line (the sigil). None of other archangels used it.
Aziraphale doesnt even know in s1 who Metatron is.
As a floating head he hasn't distinguished features of angels (golden glitter, teeth, purple eyes etc.). However, does being a floating head count as a distinguished feature?
Somehow he reminds me Death from the show Castlevania. Death was also an immortal being like vampires who was disguised as other immortal being - suspicious vampire Varney. But Death is neither vampire nor human, his nature is radically different.
If M is not an angel, does he belong to the same species that angels and demons are? Or he is totally other spirit?
Or what if he was the first spirit of shades of grey? First angel/demon who went beyond restrictions and reached kinda nirvana? First one who choose his own moral?