Rabbi Shimon Gershon Rosenberg (Shagar) (1949–2007) was a leading religious Zionist scholar and teacher, and founder and Rosh Yeshiva of Yeshivat Siah-Yitzhak, a hesder yeshiva and kollel located in Efrat, Israel. He grew up in Jerusalem, studied at the Kerem B’Yavneh Hesder Yeshiva and Yeshivat HaKotel. Later in life, Rabbi Shagar delved deeply into Kabbala and Hasidism, as he sought to combine all aspects of Torah in an authentic, interdisciplinary approach.