Metatron (also known as Lord Regent, born Enoch) is the angel who the Authority chose to take over many of his reponsibilities.
He was once a man, Enoch, son of Jared, son of Mahalalel, son of Kenan, son of Enosh, son of Seth, son of Adam. He lived to be sixty-five years old and then the Authority took him into the Kingdom of Heaven and made him his regent. This happened four thousand years ago. He is also Baruch's brother and that's how Baruch and Balthamos were able to sneak into the Clouded Mountain.
He is the main antagonist of the trilogy because unknowingly the Church worships him instead of the Authority, as Metatron is the proper leader of Heaven as the Authority surrended much of his power. Metatron does not appear in the first two novels and is not even mentioned, but he is behind the evil activities of the General Oblation Board and the Church's quest to find and kill Lyra.
Mrs. Coulter describes him as man-shaped and man-sized, although his light dazzles her eyes. Even when she asks him to hide the light a bit, he looked exactly like a man in early middle age, tall, powerful and commanding.
Metatron had many wives and was a lover of the flesh. He tells Mrs. Coulter that she is more beautiful than any of his wives, and she is able to take advantage of his weakness, and she promises to lead him to Will and Lyra's dæmons. She leads him to the edge of the Abyss where Lord Asriel is waiting. Asriel, Mrs. Coulter and their two dæmons fight a fierce battle with Metatron and finally take him to his death into the Abyss.