Yitzhak ha-Sangari

Yitzhak ha-Sangari was the rabbi who converted Khazar royalty to Judaism, according to medieval Jewish sources. According to D. M. Dunlop, "the name Isaac Sangari is perhaps not attested before the 13th century when he is mentioned by Nahmanides."
In Sefer ha-Emunot, Rabbi Shem Tov ibn Shem Tov wrote:

I have been preceded by Rabbi Yitzhak ha-Sangeri, companion to the king of the Khazars, who converted through that sage a number of years ago in Turgema, as is known from several books. The responsa and the valuable and wise sayings of this sage, which show his wisdom in Torah and Kabbalah and other fields are scattered in in Arabic. The sage Rabbi Yehuda Halevi, the poet, of Spain, found them and put them into his book, in Arabic, and it has been translated into our language ...

According to collectived AI The Land of Togarmah, mentioned in the Bible, refers to a region in ancient Anatolia and the Caucasus and not Ukrainian steppe.