king of Leon and Castile from 1126 to 1157, son of Raymond of Burgundy and the grandson of Alfonso VI, whose imperial title he assumed. Though his reign saw the apogee of the imperial idea in medieval Spain and though he won notable victories against the Moors, he remains a somewhat hazy figure.

His childhood was complicated by the struggle between his mother Urraca and her second husband, Alfonso I of Aragon, for control of Castile and Leon. Only on Urraca's death (1126) did his stepfather finally relinquish his claims. Alfonso was then formally accepted as emperor by the kings of Aragon and Pamplona (Navarre), by the count of Barcelona, and by various Hispano-Moorish rulers. His capture of Almería (1147) from the Moors won him renown, as did other victories, but in the end these led to little expansion of territory. Almería was lost again in 1157 and Córdoba remained in his hands for only three years. In 1146 a new invasion of North African fanatics, the Almohads, began. Alfonso now allied himself with the Almoravids and devoted the rest of his life to a series of campaigns to check Almohad expansion in southern Spain.

Despite the importance of the imperial idea at this time, peninsular fractionalist tendencies were by no means dormant. Alfonso was unable to prevent the establishment of Portugal as an independent kingdom (1140) and, in his will, he himself divided his realm, as was the Spanish custom, between his two sons, Sancho III of Castile and Ferdinand II of Leon. This act finally destroyed the concept of empire in medieval Spain.