he was born in jerusalem in 1928 to rabbi aharon fisher, a prominent member of the perushim community. he was named after the political activist jacob israël de haan who had been assassinated four years earlier. as a teenager he studied in the etz chaim yeshiva and became a close student of rabbi isser zalman meltzer. he was later married to the daughter of rabbi zelig wallis and they settled in batei horodno area of jerusalem.