Rabbi Yosef ben Ephraim Karo, known as Maran or the Mechaber, was born in Toledo in 1488. As a child he was expelled from Spain with his family in 1492; they reached Lisbon, left it in 1497 and arrived in Istanbul in 1498. After his father's death he grew up in the home of his uncle, Rabbi Yitzchak Karo. He then spent time in Egypt and lived between Salonica, Nicopolis, Adrianople and Istanbul, before settling in Safed in 1536, where he headed the rabbinical court and a great yeshiva.

It was in Adrianople, in 1522, that he began the Beit Yosef, a vast commentary on the Tur examining every opinion of the halachic authorities, on which he worked for more than twenty years. From it he distilled the Shulchan Aruch ("the set table"), a concise code of all practical halacha. Supplemented by the Rema's glosses for Ashkenazim, it became the universal law code of the Jewish people. He also wrote Kesef Mishneh on the Rambam's Mishneh Torah, and he is regarded as opening the era of the Acharonim.

A great kabbalist, he reported that a maggid, a heavenly voice, came to teach him; these revelations are recorded in Maggid Meisharim. He passed away on 13 Nisan 5335 (1575) and rests in the old cemetery of Safed.