Answer
Yusuf ibn Tashfin, the Almoravid sultan, emerged as a formidable rival to Alfonso VI, the King of León and Castile. Their rivalry was marked by a series of conflicts, including the Battle of Sagrajas in 1086, which established the Almoravids as a dominant power in the Iberian Peninsula. Yusuf's military prowess and political acumen posed significant challenges to Alfonso's ambitions and shaped the course of medieval Iberian history.