Rabbi Yoel Kahn, who as leading disciple of Rabbi Menachem Mendel Schneerson, the revered leader of the Lubavitch Hasidim, had the uncanny ability to memorize virtually verbatim the grand rabbi’s hourslong speeches and discourses, which he then compiled into roughly 150 published volumes, died July 15 in Manhattan. He was 91.

From Rabbi Schneerson’s ascension to the leadership of the movement in 1951 until his death in 1994, Rabbi Kahn dedicated himself to preserving a record of the leader’s speeches, off-the-cuff talks, and other teachings, regarding them as the collective wisdom of a modern-day Talmudic sage or prophet. Rabbi Schneerson would expound in Yiddish on passages of Torah, Talmud and kabbalah, or on Hasidic philosophy, ethical behavior and world events, always without notes or written text. Rabbi Kahn, with a memory described as photographic, was able to recall the grand rabbi’s words in their entirety.