Rabbi David ben Zimra, known as the Radbaz (רדב"ז) was born in Spain in 1479. At the age of 13, when the Jews were expelled from Spain, his family moved to Israel and settled in the city of Safed (צפת). There rabbi David learned with Rabbi Yosef Zaragosi, the Rabbinical leader of the Jewish community of Safed at the turn of the century.
In 1517 he moved to Egypt where he was appointed as the Hakham Bashi, or Chief rabbi of Egypt, a position that he held for over forty years. The Radbaz was a man of independent means. He was a successful merchant, dealing with wheat and leather. He amassed a considerable fortune, which allowed him to support his own Yeshiba. Some of the students of that Yeshiba were great luminaries, like rabbi Betsalel Ashkenazi (שיטה מקובצת) , rabbi Isaac Luria (the Ari haqadosh), rabbi ya'aqob Castro ( מהריק"ש) .
Upon attaining the age of 90, the Radbaz resigned the chief rabbinate in Egypt. He distributed his fortune among the poor, making special provision for Tora scholars, and moved to Erets israel. He settled in Safed and became an active member of the rabbinical court presided over by rabbi Yosef Karo. The Radbaz died in Safed in 1573.
His most important book, she-elot utshubot Radbaz, is a collection of ver 3000 Rabbinical expositions and response.
A few illustrations:
In one of his most famous responses (4:219) he discusses the origin of the Jews of Ethiopia (פלאשים) which he considered legitimate Jews (see this interesting article in English).
He also wrote about the exact place and identification of the Temple mountain (הר הבית) and authorized the access to it.
The Radbaz reintroduced in the Egyptian synagogues the tradition to repeat aloud the Amida (חזרת הש"ץ) in accordance with the older tradition.
He also replaced the old Jewish Civil Calendar used among Egyptian and Babylonian Jews since the time of the Second Bet haMiqdash (מניין שטרות, the Seleucid calendar, year 1=312 BCE. See here). The Radbaz reintroduced the custom of counting the years from the Creation of the world, as was widely in use among Jews in most other countries and as it is used by all today.
Download Teshubot haRadbaz here.
Some other works by Radbaz
דברי דוד Dibre David ("Words of David") - containing decisions and hiddushim (original Torah thoughts) on Mishne Tora.
יקר תפארת Yeqar Tif-eret ("Honor of Excellency") - refuting the criticisms Rabbi Abraham ben David (Ra-abad) on Maimonides, which the Maggid Mishne overlooked.
כללי הגמרא Kelale ha-Gemara ("Rules of the Talmud) - a book on the methodology of the Babylonian Talmud.
דיני רבה וזוטרא Dine Rabba ve-Zutra ("The Great and Small Decisions") - a commentary on the shulhan 'arukh.