Metatron, also known as Lord Regent, is the enforcer of the Authority's will and vehemently attack all those who question it. He is portrayed by Pullman as a tyrannical leader of blind faith. Pullman keeps to some factual aspects, such as the fact that he was initially the human Enoch. Metatron is literally said to be the voice of God and led the people of Israel through Egypt.
Interestingly, Metatron is linked through geometry to the Tree of Life and the theme of the fall of man. Metatron's Cube is a geometric shape that is considered a holy glyph and the symbol of Metatron himself. It is formed from the symbol of the Fruit of Life pattern, you can see this process in the video below.