Ya'qub ibn Ibrahim al-Ansari (Arabic: يعقوب بن إبراهيم الأنصاري, romanized: Yaʿqūb ibn Ibrāhīm al-Anṣārī), better known as Abu Yusuf (Arabic: أبو يوسف, romanized: Abū Yūsuf) (d.798) was a student of jurist Abu Hanifa (d.767) who helped spread the influence of the Hanafi school of Islamic law through his writings and the government positions that he held. He served as the chief judge (qadi al-qudat) during reign of Harun al-Rashid. Kitab al-Kharaj, a treatise on taxation and fiscal issues facing the state, is his most well-known publication. Source: Wikipedia (en)