Yitzchak Sagi Nahor (Isaac the Blind) was a Provençal rabbi and kabbalist. He was the son of Ra'avad, and was active at the time that "Sefer HaBahir" was first emerging in public. In some circles, he was considered its author. His students, Rabbi Azriel and Rabbi Ezra, taught Kabbalah to Ramban. Rabbeinu Bachya calls him "the father of Kabbalah."