Answer:
   
   The Zohar [radiance] is the greatest classic of Jewish mysticism. It
   is a mystical commentary on the Torah, written in Aramaic, and is
   purported to be the teachings of the 2nd century Palestinian Rabbi
   Shimon ben Yohai. Legend relates that during a time of Roman
   persecution, Rabbi Shimon hid in a cave for 13 years, studying Torah
   with his son; During this time he is said to have been inspired by G@d
   to write the Zohar. However, there is no real mention of this book in
   any Jewish literature until the 13th century.
   
   In the 13th century, a Spanish Jew by the name of Moshe de Leon
   claimed to discover the text of the Zohar, and the text was
   subsequently published and distributed throughout the Jewish world.
   
   However, there is a school of thought (based on the writings of
   historian Gershom Scholem) that de Leon himself was the most likely
   author of the Zohar. Among other things, Scholem noticed the Zohar's
   frequent errors in Aramaic grammar and its highly suspicious traces of
   Spanish words and sentence patterns. This is still highly disputed by
   most (but not all) Orthodox Jews.
   
   Whoever the author is, the content of the book is not fraudulent. It
   definitely is based on older works, and it was a common practice to
   ascribe the authorship of a document to an ancient rabbi in order to
   give the document more weight.
   
   The Zohar contains and elaborates upon much of the material found in
   'Sefer Yetzirah' and 'Sefer Bahir', and without question is the
   Kabbalistic work par excellance.