Yaqub ibn Ibrahim al-Ansari, better known as Abu Yusuf (Arabic: أبو يوسف) (d.798) was a student of legist Abu Hanifah (d.767) who helped spread the influence of the Hanafi school of Islamic law through his writings and the government positions he held.
He served as the chief judge (qadi al-qudat) during reign of Harun al-Rashid. His most famous work was Kitab al-Kharaj, a treatise on taxation and fiscal problems of the state.
Read more about Abu Yusuf: Biography, Literary Works, Doctrine and Methodology, List of Works