Israel Joshua Singer was a successful and widely-read writer before his younger brother I. B. Singer became known as the defining writer of the Yiddish world. The older brother was eventually eclipsed by the younger. I. J. Singer worked as correspondent for the Jewish Daily Forward beginning in 1921; he eventually obtained work there for his brother.
I. J. Singer's novel The Brothers Ashkenazi is a painful book to read, at least I found it so, as it stresses the stark realities of life in Poland between the wars. If I remember correctly, The Family Carnovsky – about German Jews -- is even more painful! Like many Yiddish writers, he's important if you are trying to develop an understanding of Jews in Eastern Europe before the War.