Rav Hai Gaon was the last of the Geonim of Pumbeditha. With him came to an end the era of the Geonim (the brilliant Talmudic scholars who headed the great Yeshivot of Sura and Pumbeditha) that lasted nearly 450 years (The Geonim who flourished in Babylonia (from about 4350 to 4800) were the successors to the Rabbanan Seburai (about 4260-4350), who in turn succeeded the Amoraim (about 3980-4260), after the completion of the Talmud Bavli, 4260). He was the son of his equally famous father, Rav Sherira Gaon, head of the Yeshiva of Pumbeditha (a small town near present-day Baghdad, the capital of Iraq).

Rav Hai grew up under the care and tutelage of his great father. While still a young man, he became famous for his extraordinary mastery of the entire Talmud and the writings of the generations of Geonim, which were carefully preserved in the archives of the Yeshiva. Under the influence of the works of Rav Saadia Gaon (last but one of the Geonim of Sura, who died in 942), Rav Hai became proficient also in the sciences and various languages.

At the age of 48, Rav Hai was appointed as Av Bet Din (Head of the Highest Court), second highest office, next to the Gaon. Thus, father and son held the two highest offices in the leadership of the Jewish people at the same time, until Rav Hai succeeded his illustrious father as Gaon of Pumbeditha, a short time before his father passed away (in 998).

The Yeshiva of Pumbeditha was the spiritual nerve center, so to speak, of the Jewish people. The head of the Yeshiva was the recognized highest Torah authority not only of Babylonian jewry, but of all the Jewish people the world over. Wherever and whenever there arose any question about any Jewish law and custom, or about the proper interpretation of any text or passage of the Talmud, and the like, it was to the heads of the Yeshiva in Pumbeditha that the question was addressed. Records of such questions and answers were preserved in the Yeshiva archives for future reference and decisions. During the reign of Sherira and Hai, numerous questions and inquiries came from near and distant Jewish communities addressed to both of them jointly, which were answered in their names. Later, after Rav Hai was elected to the office of the Gaonate, inquiries were addressed to him. Being the last of the Geonim, and having occupied this high office with distinction for 40 years, it was rightly said of Rav Hai that "he was the last of the Geonim in time, but the first in importance."

Towards the end of Rav Sherira's life (he, too, lived nearly one hundred years), a great calamity happened to him and his son, when they were both arrested by the Caliph on the basis of an accusation that they were disloyal to him. The Caliph also ordered that all their possessions be seized. For a time, they and all of Babylonian Jewry, were in serious danger. However, before long both the father and son were cleared of the accusations. They were freed and permitted to continue in their high offices, and their properties were returned to them.

This terrible ordeal had gravely undermined the health of the aged Gaon. He decided to step down and let his illustrious son take over the duties of the Gaonate.

The question of who would succeed Rav Sherira as the Gaon of Pumbeditha had been under consideration for some time, for there was another worthy contender for this high office. He was Rav Shmuel ben Hofni, a member of a distinguished family which, like that of Rav Sherira's, traced its descent from the Royal House of King David. Moreover, several ancestors of Rav Shmuel served as Geonim of Pumbeditha, namely his great grandfather Rav Yosef, grand­father, Rav Kohen Tzedek, and the latter's son (Rav Shmuel's uncle) Rav Nehemiah - all held this highest office. Rav Shmuel's father, Rav Hofni, held the office of Av Bet Din, second only to the Gaon. Being also older than Rav Hai, he had many supporters who thought he was entitled to be crowned as the Gaon of Pumbeditha. The problem was happily resolved, however, when the two families were united through the marriage of Rav Hai to the daughter of Rav Shmuel and Rav Shmuel ben Hofni became Rosh Yeshiva and Gaon of Sura. This famous academy had been closed for some years as a result of the dispute between the Exilarch (Nassi) David ben Zakkai and Rav Saadia Gaon. Now it was reopened under the newly elected Rosh Yeshiva Rav Shmuel ben Hofni. Rav Hai thus remained the unanimous choice to succeed his father as the Gaon of Pumbeditha, and when Rav Sherira stepped down, Rav Hai was crowned as Gaon.

Soon afterward, Rav Sherira died (at the ripe old age of 98 years). It has been recorded that in honor of Rav Hai Gaon, the Haftarah that was read the following Shabbat was taken from I Kings, ch. 2, and instead of reading the words, "And Shlomo sat upon the throne of David, his father; and his kingdom was established firmly" (I Kings, 2:2), the reader read: "And Hai sat upon the throne of Sherira, his father; and his kingdom was established firmly."

Rav Hai served as Gaon of Pumbeditha for forty years, until his death (on 20th of Nissan 4798/1038), at the age of 99 years.

Rav Hai was greatly revered by all Jews in all lands, from Persia and Turkey in the East to Spain in the West. The greatest Torah scholars of his time, such as Rabbi Shlomo ben Yehuda in the Land of Israel, Rabbeinu Nissim of Kairwan (North Africa), the latter's disciple, Rabbi Shmuel Hanagid of Spain, and other scholars and communal leaders in various parts of the world sent him inquiries and accepted his opinions and rulings as the highest authority. These Halakhic opinions - Teshuvot, Responsa made a substantial addition to the Responsa literature of the Geonim that preceded him. Indeed, nearly half of all the Geonic Responsa was written by Sherira and Hai. These two Geonim wrote about 1000 Responsa. These Responsa were usually written in the language of the inquiry: in Hebrew, Aramaic, or Arabic.

In addition to the Responsa, Rav Hai Gaon wrote many Halakhic works, mostly in Arabic, the spoken language of most Jews in the Arab land. Some of these were later translated into Hebrew. Several of his works have been preserved in part, either in the original Arabic or in Hebrew translation, or in both. Some have been published with commentaries by other scholars. He has also been frequently quoted in other Rabbinic works.

Among Rav Hai's major works, in addition to the Responsa, are the following:

Mishpat Shavuot or Shaarei Shavuot, "Laws of Oaths," which had been translated by an unknown trans­lator from Arabic into Hebrew. It was printed for the first time in 5362 (1602) in Venice.

Sefer Mekach uMimkar, "Book of Purchases and Sales," published with a summary of a separate work, "Laws of Loans." This work, comprising 60 chapters, was translated from Arabic into Hebrew by Rabbi Yitzhak al Barceloni. The original Arabic text was lost.

These and other works deal with different aspects of business laws, such as contracts, agreements, litigations, and related subjects that come under the classification of Civil Law.

He also wrote works in the area of the dietary laws, such as the "Book of the Forbidden and the Permitted"; on the laws of Shechitah; on the laws of Tefillin; and other areas of the everyday Jewish life.

Rav Hai also wrote commentaries on T'NaCh, Mishnah and Gemara. He wrote commentaries on at least seven tractates of the Talmud. Of all these works only parts have been preserved.

He also composed religious poetry in the form of Piyyutim and Selichot. An expert grammarian, he wrote treatises on Hebrew and Arabic grammar.

Clearly, Rav Hai was an accomplished scholar in many fields. It would be difficult to evaluate fully his many and lasting. contributions in the field of Halachah, in the interpretation of the Talmud and the Holy Scriptures, the history and development of Jewish Tradition, Jewish customs and prayers. Divine Providence blessed this great sage with a long and fruitful life and with extraordinary talents, so that, as the last of the Babylonian Geonim, he could transmit the spiritual treasures of the crucial Geonic era to succeeding generations. He was thus one of the main links in the unbroken golden chain of the Massorah (Tradition) from Moshe Rabbeinu, the Prophets and the Men of the Great Assembly, through the Tannaim and Amoraim and their successors, the Geonim. This link was all the more important as it forged the smooth transition from the Talmudic to the post-Talmudic era, at a time when the center of Jewish life was moving from the East to the West.

Rav Hai's work was continued by his many disciples and leading Torah authorities of the next generation. The respect and reverence which Rav Hai enjoyed in the Jewish world of his time and thereafter is also reflected in such titles attached to his name as "Father of Israel" and "Teacher of all Jews."