Al-Fadl ibn al-Rabi', born in 757–8 CE, is the son of al-Rabi' ibn Yunus, a former slave who had risen to occupy the influential post of chamberlain (hadjib) under caliphs al-Mansur (r. 754–775) and al-Mahdi (r. 775–785).
Rabi's power relied on his control of the access of outsiders to the Caliph, as well as his de facto leadership of the Caliph's numerous and influential mawla (servants, freedmen).
Fadl had effectively inherited his father's position at court, and benefited from the high esteem in which Harun al-Rashid held him: upon his accession, the Caliph placed Fadl in charge of his personal seal, and in 789–90 he was made head of the diwan al-Nafaqat (the "Bureau of Expenditure").
In 795–6, he was named to his father's old post of hadjib, reportedly after succeeding in finding the poet Ibn Jami, who had been exiled under al-Hadi (r. 785–786).
Fadl, utterly loyal to his master, serves as Harun's trusted agent.
Despite his apparently good personal relations to the Barmakid patriarch Yahya ibn Khalid, stories portray Fadl as the Barmakids' chief rival at court.
Following the fall of the Barmakid family from power, Fadl had succeeded Yahya as wazir, in effect becoming the Caliph's chief minister and advisor.
However, Fadl lacks the almost plenipotentiary powers that Harun had granted Yahya, and his remit is limited to a supervisory role over expenditure and in the handling of petitions to the Caliph, while the actual financial administration is entrusted to another official.
As vizier, al-Fadl ibn ar-Rabi' lacks the efficiency of the Barmakids, and the personal decisions of Harun may carry more weight.
The Caliphate has conducted further successful operations against the East Roman Empire, but Harun falls ill at Tus (near modern Meshed) in the autumn of 808, while on his way to Khorasan to deal personally with the serious two-year-old revolt of Rafi ibn al-Layth.
