Abu al-Aswad al-Du'ali

Abu al-Aswad ad-Duʾali (Arabic: أَبُو ٱلْأَسْوَد ٱلدُّؤَلِيّ, Abū al-ʾAswad al-Duʾalīy; c.-16 BH/603 – 69 AH/688/89), whose full name was ʾAbū al-Aswad Ẓālim ibn ʿAmr ibn Sufyān ibn Jandal ibn Yamār ibn Hīls ibn Nufātha ibn al-ʿĀdi ibn ad-Dīl ibn Bakr, surnamed ad-Dīlī, or ad-Duwalī, was a tabi'i, the poet companion of Ali ibn Abi Talib and was one of the earliest, if not the earliest, Arab grammarians. He is known for writing the earliest treatise on Arabic grammar, through study of the Quran, explaining why he is sometimes known as the "Father of Arabic Grammar."

ad-Du'alī is said to have introduced the use of diacritics (consonant and vowel markings) to writing, and to have written the earliest treatises on Arabic linguistics, and grammar (nahw). He had many students and followers.

With the expansion of the early Islamic Empire, with new converts to Islam wishing to be able to recite and understand the Quran, the adoption of a formalised system of Arabic grammar became necessary, and ad-Du'ali helped develop it, such as with the concepts of Nahw and Taskheel. His science of grammar led in turn, to the establishment of the first great School of grammarians at Basrah, that would be rivalled only by the school at Kufah.