Sa'adiah ben Yosef Gaon, ("Sa`īd bin Yūsuf al-Fayyūmi"); was a prominent rabbi, Jewish philosopher, and exegete of the geonic period. Saadia is known for his works on Hebrew linguistics, Halakha, and Jewish philosophy. In his philosophical work "Emunot v'Dayot" is represented the first systematic attempt to integrate Jewish theology with components of Greek philosophy. Saadia was also very active in opposition to Karaism, in defense of rabbinic Judaism. Wikipedia
The definitive Wikipedia entry for Saadia Gaon. Wikipedia is the biggest multilingual free-content encyclopedia on the Internet. en.wikipedia.org/wiki/Saadia_Gaon
Saadya Gaon (Saadya ben Joseph, known in Arabic as Sa'id ibn Yusuf al-Fayym) was born in Fayym (upper Egypt) in 882 and died in Baghdad in 942. plato.stanford.edu/entries/saadya/