Rav Saadia Gaon רב סעדיה גאון
Gaon of Sura, first Jewish philosopher, translator of the Torah into Arabic
Rav Saadia was born in Egypt around 4642 and was an outsider in the Babylonian system: Geonim came from old families, and he rose to head the academy of Sura on learning alone.
His first battle was over the calendar. When Aaron ben Meir of the Land of Israel tried unilaterally to shift the festival dates, Saadia fought and preserved a single reckoning for the whole people. His second battle was with the Karaites, who rejected the Oral Torah; his systematic polemics are credited with halting their growth.
He translated the Torah into Arabic with commentary — the Tafsir — so that Arabic-speaking Jews could read Scripture in their own language. He wrote «Emunot ve-Deot», the first book to set out the foundations of faith in philosophical order. He compiled the first systematic prayer book, and early works of Hebrew grammar and lexicography.
He quarrelled with the exilarch David ben Zakkai, was deposed, and wrote his greatest books in those years of retirement. They were later reconciled. He died in 4702.