Saadia Ben Yosef Alfiomi Gaon (882 - 942) also called Saadia HaPiomi after his homeland Fayum in Egypt, and in short Rasag (רס"ג), one of the geniuses of Babylon, Rosh Yeshivat Sura. Rabbi Saadia Gaon has a high level of interpretation of the Torah and a judge of Halacha in the history of Judaism. He developed a very great literary action and wrote books on matters of the Hebrew language and grammar, piyyutim, and philosophical essays. Rasag is also the first to deal with the grammar of the Hebrew language in an orderly fashion, under the influence of the grammarians of Arabic who were active at the time. He is therefore considered the first of the medieval grammarians.
Philosophy: The most important and largest of his books is his philosophical book - "The Book of Beliefs and Opinions". This book deals with the following topics: the creation of the world, the reality of God, the flavors of the commandments, providence, redemption, the written Torah and the Torah, the religions, the philosophies, the next world, reward and punishment, morality and more. , Islam, Christianity, Zarathustra belief, sensualism, atheism, as well as cosmological and psychological conceptions that are inconsistent with Judaism. He accepted the method of "mazatla" (philosophical current in Islam) regarding the freedom of will and unity of God, but rejected the atomic theory of the "kalam" (philosophical movement in Islam). In psychology, he blends Aristotle and Plato. Religious truth is a revelation and the content of revelation is the same as the intellect, the mind can know the content and truth of revelation. There is a religious mitzvah to achieve in our minds what comes to us in prophecy. And all this else we will receive the true software of revelation as the basis for faith. The sources of knowledge are: the senses, the intellect, the necessity and the tradition. Rasag went in the ways of the "prisoner" to prove the reality of the Creator from the renewal of the world. Rasag rejects the reality of "primordial matter" as the root of the complexity of the world. The first to explicitly divide between mental and auditory commandments. According to him, the mind is not a random (contingent) feature of the body, but a bone (substance) close to the wheels of the sky.
Siddur Rasag - סידור רס"ג: One of the first siddurs written. It also includes halakhic material, and material from Rasag poetry.
Sefer HaMitzvot: did not reach us (except for a few passages), but Rasag also wrote a piyyut for Shavuot that included the thirteen mitzvot ("warnings").
סידור רס"ג: אחד הסידורים הראשונים שנכתבו. הוא כולל גם חומר הלכתי, וחומר משירת רס"ג.
ספר המצוות: לא הגיע לידינו (מלבד קטעים בודדים), אולם רס"ג גם כתב פיוט לשבועות שכלל את תרי"ג המצוות ("אזהרות").