Zohar זוהר
The foundational book of kabbalah, ascribed to Rabbi Shimon bar Yochai and published in Spain in the thirteenth century.
The Zohar is written in a distinctive Aramaic and shaped as a commentary on the Torah — but a commentary that sees behind every narrative the structure of worlds, the ten sefirot, the relation of the masculine and feminine in creation, the exile of the Shechina. Formally it recounts Rabbi Shimon bar Yochai and his students walking through the Galilee and speaking of the Torah's secrets.
Tradition dates it to Rashbi's time, to the years in the cave. In its known form it was published in Castile at the end of the thirteenth century by Rabbi Moshe de Leon, and what in it is ancient and what later has been debated for seven centuries.
Its influence is enormous: the Arizal, Tzfat, hasidism, Lecha Dodi, the vigils of Shavuot and the seventh night of Pesach all grew from it.