Rema — Rabbi Moshe Isserles הרמ"א — רבי משה איסרליש
author of the «Mappah», the Ashkenazi glosses to the Shulchan Aruch
Rabbi Moshe Isserles was born in Kraków around 5290 into a wealthy and learned family and became head of the yeshiva and rabbi of the city. When Rabbi Yosef Karo's Shulchan Aruch reached Poland he saw the problem at once: the book was superb, but decided by Sephardi authorities, while Ashkenazi communities had lived for centuries by different customs.
He could have written his own code, and nearly did — his «Darkei Moshe» comments on the Tur from the Ashkenazi side. Instead he chose something else, and it proved momentous. He added short glosses to the Shulchan Aruch — the «Mappah», a tablecloth for the set table: «but our custom is…», «and so it is practised in these lands». Printers began issuing both texts together, and ever since Jewish law has been one book with two voices.
It was an acknowledgement that a community's custom is not a deviation but part of the law.
He also defended the study of philosophy, and was criticised for it.