Considered one of the most significant rabbis in Jewish history and Gadol HaAchronim. The Gaon, as he was known amongst his students, had and unimaginable influence on halachic rulings and the interpretation of rabbinic, halachic and Kabbalistic writings. He was a vehement opposer of the hassidic movement headed by the Baal Shem Tov and founded the Mitnagdim school of thought.