Yusuf ibn Tashfin was the founder of the Almoravid empire in its imperial form and one of the most consequential rulers of the medieval Berber world. Born among the Lamtuna of the western Saharan Sanhaja, he was deputised in 1061 by his cousin Abu Bakr ibn Umar to govern the northern provinces of the Almoravid movement while Abu Bakr returned south to suppress a Saharan rising.
Around 1070 Yusuf founded a permanent capital at the Haouz plain south of the High Atlas. Marrakesh — Mṛṛakec — was conceived as an administrative seat free of the dynastic ambitions of the older Berber cities. When Abu Bakr returned in 1072 from the south, finding the kingdom consolidated and Yusuf's authority entrenched, he formally ceded leadership of the northern empire and returned to Saharan operations until his death in 1087.
Under Yusuf the Almoravid empire took its full form. Fes fell to him in 1075 and was given a new walled enclosure; Tlemcen and Algiers followed. In 1086, summoned by the taifa kings of al-Andalus to oppose the Christian advance, Yusuf crossed the Strait and defeated Alfonso VI of León-Castile at the Battle of Sagrajas. Subsequent campaigns absorbed the Andalusi taifas under direct Almoravid administration. By his death in 1106 the empire reached from the Senegal river to the Ebro, the first Berber-led state to govern both the Maghreb and the Iberian peninsula.
Yusuf is preserved in Berber and Andalusi memory as a figure of unusual personal asceticism — the Almoravid sources stress his refusal of palace and ceremonial — and as a competent military and administrative organiser. His successors maintained the empire for another four decades before its fall to the Masmuda Almohads in 1147.