Rav Hai Gaon רב האי גאון

He headed Pumbedita after his father and held the office until his death in 1038. His responsa — hundreds of them — went out across the Jewish world and largely determined the shape of practical law.

What set him apart was his sobriety. He wrote readily about what he did not know; he argued with the legends circulating about earlier geonim; he was cautious about magical practices and about what today would be called folk mysticism. Of the story of Rav Natronai's miraculous journey to Spain he said that it had not happened.

He knew Arabic and Greek philosophy, corresponded with Spain and North Africa, and through that correspondence Babylonian learning passed to the new centres — just as the academies themselves were fading.

Abraham ibn Daud, in Sefer HaKabbalah, calls him the last of the geonim. Formally there were geonim after him, but the era ends with him: the centre of gravity moves to Kairouan, Spain and the Rhineland, and the time of the rishonim begins.