Saadia Gaon

Saʿadia ben Yosef Gaon or Said bin Yusuf al-Fayyumi (892–942) was a prominent rabbi, gaon, Jewish philosopher, and exegete who was active in the Abbasid Caliphate.

Saadia is the first important rabbinic figure to write extensively in Judeo-Arabic. His extensive writings are one of the foundations of Judeo-Arabic literature. Known for his works on Hebrew linguistics, Halakha, and Jewish philosophy, he was a student of the philosophical school known as "Jewish Kalam". In this capacity, his philosophical work entitled The Book of Beliefs and Opinions represents the first systematic attempt to integrate Jewish theology with components of ancient Greek philosophy. Saadia was also very active in opposition to Karaite Judaism in defense of Rabbinic Judaism.

Notable works: Tafsir, Emunoth ve-Deoth, Siddur of Saadia Gaon

Source: Wikipedia — https://en.wikipedia.org/wiki/Saadia_Gaon