Yehudah Aryeh Leib Alter, also known by the title of his main work, the Sfas Emes or Sefat Emet שפת אמת‎, was a Hasidic rabbi who succeeded his grandfather, Rabbi Yitzchak Meir Alter, as the Av beis din and Rav of Góra Kalwaria, Poland, and succeeded Rabbi Chanokh Heynekh HaKohen Levin of Aleksander as Rebbe of the Gerrer Hasidim. Wikipedia