Mordechai Yissachar Ber Leifer (Hebrew: מרדכי יששכר בער לייפער; 1955 – 4 October 2020) was the third Rebbe of the Pittsburgh Hasidic dynasty.

He also shepherded Pittsburgher Hasidim in Jerusalem, Bnei Brak, Beit Hilkia, New York City, and California.

[2][5] At the time of his birth, his father was teaching Torah and Hasidut and eventually founded a Hasidic yeshiva in Newark.

[1] He also established charitable institutions in the city, which earned him a special commendation as "Worthy Citizen of Ashdod" from Mayor Yehiel Lasri.

[3][12][13] In total, Leifer composed more than 250 melodies, many of them pertinent to the synagogue prayer service, especially the Hallel on Rosh Chodesh and Yom Tov.

[3] For the first six months of the COVID-19 pandemic in Israel, Leifer stayed close to home and strictly adhered to Ministry of Health guidelines.

[18] The Rebbe's Torah discourses have been published in two volumes, covering the years 1990 through 2010, under the title Pisgamei Oraisa–Shabbos (Hebrew: פתגמי אורייתא-שבת).

[3] This series also includes ten volumes of Leifer's discourses on the weekly Torah portion and Jewish holidays.