Rabbi Chaim ben Isaac of Volozhin
Rabbi Chaim of Volozhin was the outstanding disciple of the Vilna Gaon and the founder of the Volozhin Yeshiva in 1802, the most important and most influential Lithuanian institution. Reb Chaims philosophy is expounded in his Nefesh HaChaim where he emphasizes the power of Torah study and fulfillment of mitzvos to bring a Jew close to G-d. In a famous section of that work, he takes issue with those (an obvious reference to Hasidim) who see dveikus, or cleaving to G-d, as a prerequisite to fulfillment of mitzvos. The central importance of Torah study reached its heights in the yeshiva, which became a model for all Lithuanian Yeshivos.
Source: Orthodox Union