Joseph Rosen (Yiddish: יוסף ראָזין, Yosef Rosin; 1858 – 5 March 1936) known as the Rogatchover Gaon (Genius of Rogachev) and Tzofnath Paneach (Decipherer of Secrets—the title of his main work), was a rabbi and one of the most prominent talmudic scholars of the early 20th-century. Rosen was known as a gaon (genius) because of his photographic memory and tendency to connect sources from the Talmud to seemingly unrelated situations. Rosen has been described as the foremost Talmudic genius of his time. Biography Joseph Rosen was born in Rogachov, now Belarus, into a Hasidic family of Chabad-Kopust Hasidim, and was educated in the local cheder (elementary school). His unusual capabilities were noticed at the age of 13, when he was sent to study in Slutsk along with Chaim Soloveitchik (5 years his senior), under Yosef Dov Soloveitchik (Beis Halevi). He subsequently studied under Yehoshua Leib Diskin (Maharil Diskin) in Shklov. In 1889, he assumed the rabbinate of the Hasidic community in Dvinsk for almost 50 years, where his non-Hasidic counterpart was Meir Simcha of Dvinsk. They served in parallel until the late 1920s, and enjoyed excellent relations. Among those who received semikha (rabbinic ordination) from him were Menachem Mendel Schneerson (the seventh Lubavitcher Rebbe, 1902-1994), Mordecai Savitsky (1911-1991) of Boston, Zvi Olshwang (1873–1961) of Chicago (brother-in-law of Shimon Shkop) and Avraham Eliyahu Plotkin (1888-1948; author of Birurei Halachot—a copy of the actual semikha is included in that work). Rosen is remembered for his breadth of Torah knowledge and caustic wit. He did not suffer inadequacy lightly. He was similarly reputed to rarely quote any rabbinic authority post-Maimonides, and avoided recent rabbinic works of the Acharonim in favour of the Rishonim (those preceding the late 15th century). His responses to queries of Jewish law are generally enigmatic and cryptic. Rosen died in Vienna in 1936 at the Vienna Sanitorium and his body was sent to Dvinsk for burial. Throughout his life, despite not being an official Lubavitcher Hasid, he maintained very close connections to Lubavitcher Hasidim and their rebbes Sholom Dovber Schneersohn and Yosef Yitzchak Schneersohn. After Sholom Dovber's death, he supported the decision to appoint the young Yosef Yitzchak as the new Rebbe. Rosen is a famous figure in Chabad-Lubavitch folklore. His name often comes up in stories told in yeshivas and during farbrengens (Hasidic gatherings). Stories range from self-sacrifice and dedication to Torah values despite the pressures of the