Abul Hasan Jawhar bin Abdullah traced his origin from his country of birth, Sicily in Italy. Imam al-Muizz had given him the kunya of Abul Hasan, and was also called al-Katib (secretary) and al- Qaid (general). He was born most probably between 298/911 and 300/913 in Sicily, the then island under occupation of the Byzantines, and died most probably in 381/992.
During the period of Imam al-Mansur, Jawhar was brought as a slave to Kairwan and was presented before the Imam. Realizing his potential, he was made as a personal attendant of Imam al-Mansur, and soon rose to prominence. In 341/932, al-Muizz appointed him as his Katib and since then, he became known as Jawhar al-Katib. In 347/958, he was made the commander-in-chief of the Fatimid forces, and was assigned to subdue the remaining parts of the Maghrib. In 347/958, Jawhar led the Fatimid forces westwards and defeated near Tahrat, a large army of the Zanata Berbers commanded by Yala bin Muhammad, the chief of the Banu Ifran, and an ally of the Umayyads of Spain, who had rebelled against the Fatimids. Yala, who ruled the central Maghrib from Tahrat to Tangier was killed and thus the Ifranid influence in the central Maghrib came to an end.
He further proceeded towards Sijilmasa, then ruled by the Midrar tribe and killed its chief, Muhammad bin al-Fath in a fierce fighting. Jawhar marched against Fas after spending a year in the eastern Morocco. In 349/960, he beseiged the strongest fortress of the Umayyads. He took possession of Fas and arrested its Umayyad governor. Jawhar proceeded towards the far west, and continued conquering one after another city till he reached the Atlantic ocean. He ordered some fish to be put in a pot with water, and sent it to al-Muizz to let him know symbolically that whichever cities he had crossed, he conquered them as far as the Atlantic ocean.