Jewish physician, translator, and political figure who helped inaugurate the golden age of Hebrew letters in Moorish Spain and who was a powerful statesman in a number of major diplomatic negotiations.

After becoming court physician to the powerful Umayyad caliph ʿAbd ar-Raḥmān III (Abd al-Raḥmān IIIʿ), Ḥisdai gradually gained eminence in the Arab world, acting as vizier without title. He used his linguistic talents (he knew Hebrew, Arabic, and Latin) and persuasive personality in delicate diplomatic missions between Muslim and Christian rulers. On one occasion he helped negotiate a treaty with the Byzantine Empire. One of the presents from the Byzantine emperor to the caliph was a copy of a pharmacological text by the Greek physician Dioscorides (fl. c. AD 50); Ḥisdai helped translate it into Arabic. On another occasion, Ḥisdai paved the way for a peace treaty with the warring kingdoms of Navarre and León. After ʿAbd ar-Raḥmān died in 961, Ḥisdai continued to perform important services for ʿAbd ar-Raḥmān's son and successor, al-Ḥakam II, in whose reign he died.

Ḥisdai helped inaugurate the golden age of Spanish Judaism, gathering under his patronage such major literary figures as Dunash ben Labrat (c. 920–c. 990) and Menahem ben Saruq (c. 910–c. 970), who helped establish scientific Hebrew grammar and a new mode in Hebrew poetry. Ḥisdai fostered the study of Jewish law and the Talmud (the rabbinic compendium of law, lore, and commentary), thereby making Spanish Jewry relatively independent of the Eastern Talmudic academies.

Ḥisdai's correspondence (written by Menahem ben Saruq) with a Jewish Khazar king, Joseph, is of historic importance. The Khazars, a Turkic people dwelling in southern Russia, had converted to Judaism in the middle of the 8th century AD. Ḥisdai's letter and the king's response led a shadowy existence until their unexpected publication in the 16th century. After much controversy, the authenticity of both letters and the accuracy of their information seem well established.