Sariel, name meaning the Command of God, is both a fallen Watcher, and (as Saraqael) one of the seven holy angels who is "of eternity and trembling". In Kabbalistic lore, he is one of seven angels of the earth. Origen identified Sariel as one of seven angels who are primordial powers. In Gnosticism, Sariel is invoked for his protective powers.
He was one of the leaders of angels who lusted after the daughters of men and produced the Nephilim. They descended to the summit of Mount Hermon, in the days of Jared, to acquire wives and lead men astray. Sariel specifically taught men about the course of the moon.
Knibbs' translation of the names of the Book of Enoch says it was Sariel who taught humans the "course of the moon"