Physician, philosopher, theologian, and translator. His full name is Abū Zayd Ḥunayn b. Isḥāq b. Sulaymān b. Ayyūb al-ʿIbādī, and he was known in medieval Europe as Johannitius. He was born in 808 near Ḥirta, where his father was a pharmacist. He likely grew up bilingual in Arabic and Syriac, and he acquired an excellent knowledge of Greek as well as Persian in the course of his education. Ḥunayn studied medicine in Baghdad under the famous physician Yūḥannā b. Māsawayh (d. 857), who stemmed from one of the prominent medical families of Gondeshapur (Beth Lapaṭ). In Baghdad, Ḥunayn became well-known as one of the foremost translators of Greek texts into Syriac and Arabic. In addition to his translation activity, Ḥunayn was also the personal physician of Caliph al-Mutawakkil (r. 847–61). He died in Baghdad in 873.

Ḥunayn is best known for the central role that he played in the Graeco-Arabic translation movement of the early Abbasid period (in general, see Gutas). His translation activity was carried out in conjunction with a number of his students, including his son Isḥāq b. Ḥunayn (d. 910), his nephew Ḥubaysh b. al-Ḥasan, ʿĪsā b. Yaḥyā, and Isṭifān b. Bāsīl. Ḥunayn and his school translated well over a hundred Greek medical works, including Hippocrates, Dioscorides, as well as almost the entire corpus of Galen. In addition to medicine, they translated Greek philosophical and scientific texts, including Plato, Aristotle, Proclus, and Porphyry. A number of fascinating insights into the philological method of Ḥunayn and his school can be gleaned from Ḥunayn’s ‘Letter to ʿAlī b. Yaḥyā on Galen’s books which have been translated …’ (Risāla ilā ʿAlī ibn Yaḥyā fī dhikr mā turjima min kutub Jālīnūs …; ed. with GT in Bergsträsser 1925, 1932; ET Lamoreaux). In this Letter, Ḥunayn reports that he travelled throughout Mesopotamia, Syria, Palestine, and Egypt in order to procure Greek mss. of works that he wished to translate. He often collated multiple mss. of a given work in order to obtain a sound textual basis for his translations. In his translations, he seems to have adopted a sensus de sensu approach departing from the literal verbum e verbo approach that characterized 6th- and 7th-cent. Syriac translations from Greek (see Brock; see also Greek, Syriac translations from). In some cases, Ḥunayn revised older translations, such as those by Sergios of Reshʿayna (d. 536) and Iyob of Edessa (d. ca. 835?). In other cases, however, he states that the existing translations were so poor that it was necessary for him to begin anew from the Greek. Ḥunayn translated from Greek into both Syriac and Arabic (usually via Syriac) depending on the request of his patron. In a number of cases, Ḥunayn first translated the Greek into Syriac, and after that one of his students translated the Syriac into Arabic, which Ḥunayn then corrected against the Greek.

In addition to his vast body of translation work, Ḥunayn was an important author in his own right. In his ʿUyūn al-ʾanbāʾ fī ṭabaqāt al-ʾaṭibbā, Ibn Abī Uṣaybiʿa (d. 1270) attributes 111 works to Ḥunayn (ed. A. Müller, Ibn Abi Useibia [1884], 184–200). Most of Ḥunayn’s works are in the field of medicine, and a majority of these medical works are epitomes, paraphrases, or summaries of Greek works. Among Ḥunayn’s best known original works in medicine is his ‘Introduction to medicine’ (Kitāb al-mudkhal fī al-ṭibb). The substance of this text is also found in catechetical form in his ‘Book of medical questions’ (Kitāb al-masāʾil al-ṭibbiyya), which also exists in Syriac (see Degen) and which in its Latin translation remained authoritative through the Middle Ages. In addition, Ḥunayn authored several important works on ocular medicine, including the ‘Ten treatises on the eye’ (al-ʿAšr maqālāt fī al-ʿayn; ed. with ET Meyerhof) and the ‘Book of questions on the eye’ (Kitāb al-masāʾil fī al-ʿayn; ed. with FT Sbath and Meyerhof).

Ḥunayn is said to have written several works on grammar, including ‘The rules of inflexion according to the Greeks’ (Kitāb fī aḥkām al-iʿrāb ʿalā madhab al-yūnāniyyīn), ‘Book on syntax’ (Kitāb fī al-naḥw), and ‘Book of the diacritical points’ (Kitāb al-nuqaṭ). In his ‘Catalogue’, ʿAbdishoʿ bar Brikha (d. 1318) also attributes a grammar to Ḥunayn (Assemani, BibOr, vol. 3.1, 165). In addition, Ḥunayn is said to have written several works on Syriac lexicography, including the ‘Book of similar words’ (Ktābā da-šmāhe dāmyāye; ed. Hoffmann, 2–49 along with Gottheil 1887, 61*–67*; 1889), the ‘Explanation of Greek words in Syriac’ (Puššāq šmāhe yawnāye b-suryāyā), and a Compendious Lexicon (Lehksiqāwn b-pāsiqātā). These lexicographical works laid the foundation for the Syriac-Arabic lexicon of Ḥunayn’s student Ishoʿ bar ʿAli (second half of the 9th  cent.) as well as that of Ḥasan bar Bahlul (mid-10th cent.) (see Lexicography).

Ḥunayn also authored several works of a religious character, of which the following have been edited: ‘Treatise on human destiny’ (Maqāla fī al-ājāl; ed. Samir 1991; see also his study in ARAM 31 [1991], 171–92), ‘Book on the comprehension of the truth of religions’ (Kitāb fī idrāk ḥaqīqat al-adyān; title varies; ed. with FT Cheikho; ed. Sbath 1929; ed. Samir 1997), and the related response to ʿAlī b. Yaḥyā al-Munajjim (ed. with FT Samir and Nwyia). Unpublished or lost works of a religious character include: Risāla fī dalālat al-qad(a)r ʿalā al-tawḥīd (exact meaning uncertain, but dealing with the unity of God), ‘Treatise on the creation of humanity and that it was for the benefit and favor (of humanity) that it was made needy’ (maqāla fī khalq al-insān wa-annahū min maṣlaḥatihi wa-al-tafaḍḍul ʿalayhi juʿila muḥtājan), ‘Book on the history of the world’ (Kitāb taʾrīkh al-ʿālam), and (in Syriac) ‘Chapters on the fear of God’ (Reše d-deḥlat alāhā).

Finally mention should be made of Ḥunayn’s Kitāb ādāb al-falāsifa, also known as Nawādir al-falāsifa, which is primarily a collection of sayings of Greek and Persian sages and philosophers (ed. Badawi; cf. Griffith).