Samau'al al-Maghribi,  jewish revert 2 islam

The heart of his scholarly interests was Islamic-Jewish-Christian polemics, and he gave the scholarly world critical editions and translations of three significant Arabic texts. The first of them is an attack on the Jewish religion by a twelfth century Jewish convert to Islam, Samau'al al-Maghribi--whom Moshe sometimes affectionately called his "meshummad."

http://www.library.upenn.edu/cjs/_AAJR/obituaries.html