Avraham Mordechai Alter, was also known as the Imrei Emes after the works he authored. He was fourth Rebbe of the Hasidic dynasty of Ger. The Ger Rebbe, from 1905 until his death in 1948. A participant in the foundation of the Agudas Israel in Poland. Rebbe Alter was influential in establishing a network of Jewish schools. He led over two-hundred-thousand Hasidim (followers).

Ger is a Polish Hasidic dynasty originating from the town of Góra Kalwaria, Poland, where it was founded by Yitzchak Meir Alter (1798–1866), known as the "Chiddushei HaRim". Ger is a branch of Peshischa Hasidism, as Yitzchak Meir Alter was a leading disciple of Simcha Bunim of Peshischa (1765–1827). Before the Holocaust, followers of Ger were estimated to number in excess of 100,000, making it the largest and most influential Hasidic group in Poland. Today, the movement is based in Jerusalem, and its membership is estimated at 11,859 families, as of 2016, most of whom live in Israel, making Ger the largest Hasidic dynasty in Israel. However, there are also well-established Ger communities in the United States and in Europe. In 2019, some 300 families of followers led by Shaul Alter, split off from the dynasty led by his cousin Yaakov Aryeh Alter.