יצחק בן מרדכי מרגנסבורג

Rav Yitzchak ben Mordechai of Regensburg, known by the acronym Ribam and appearing in English sources as Isaac ben Mordecai, was a Tosafist of the twelfth century whose roots lay in Bohemia and whose life’s work was done in Germany. He was born in Prague, and in his younger years he learned in Regensburg before Rabbeinu Tam and before Rav Yitzchak ben Asher HaLevi.

He was afterward appointed head of the beit din of Regensburg and was reckoned the foremost rav of the city. He wrote tosafot on most of the masechtot of the Talmud; the largest body of them to reach us is on Bava Batra, and those were carried into the first printed edition of the Talmud. He is known to have written as well on Shabbat, Pesachim, Moed Katan, Ketubot, Sotah, Gittin, Nazir, Bava Kamma and Bava Metzia. In his later years a dispute arose between him and Rav Eliezer ben Nattan of Mainz, who took issue with a number of his statements; the Ribam’s reply was couched in great respect. His practice on Rosh Hashanah was to fast, so that he would come to the evening seudah with a full appetite. Among his talmidim was Rav Ephraim ben Yitzchak of Regensburg.