The New York Times said in his obituary that Isadore Twersky bridged two worlds, making the study and practice of ancient Jewish traditions the common thread of a life as a Harvard scholar and Hasidic rabbi. In the classrooms and lecture halls of Harvard, where he was Nathan Littauer Professor of Hebrew Literature and Jewish Philosophy, Dr. Twersky was a professor personified, a bearded man whose dark suits, occasional tweeds, and dignified manner bespoke his role as an internationally renowned authority on the 12th-century Jewish philosopher Maimonides and other medieval thinkers. He taught at Harvard for 30 years, his most popular course being called "Modernation and Extremism." At home in suburban Brookline and in his long black kapote at Congregation Beth David, he was every inch the dynastic Talner rebbe, the spiritual leader of a small Hasidic community his father had led a generation earlier, even as their Twersky ancestors had led congregations in Chernobyl, Ukraine, for centuries. Joseph Hacker characterized Dr. Twersky as "a historian of ideas and a researcher of the intellectual history of the Jews."