The title is pretty much self-explanatory. I know that Christianity doesn't support the existence of Metatron, as the Scripture in which Metatron is mentioned isn't a part of the Christian Bible. However, some branches of Jewish liturgy might (I don't know so I am asking) bear more specification on this fascinating subject. Please specify the first mention (chronologically) of the Metatron in the Scripture and comprehensively present his role in the grand scheme of things.
Thank you in advance.