 His father was Rabbi Yitzhak Peretz.At the age of 19, he edited the periodical "Degel Ha'Torah", the mouthpiece of the Polish branch of Agudath Israel.In 1924, in response to a call from the Ger Rebbe, Rabbi Avraham Mordechai Alter, Kasher moved to Jerusalem, in Mandate Palestine, to establish the Sfas Emes Yeshiva in honour of the Rebbe's father, Yehudah Aryeh Leib Alter.