Abd-ar-Rahman III, Emir and Caliph of Cordoba (912 - 961) was the greatest and the most successful of the princes of the Ummayad dynasty in Spain. He ascended the throne when he was barely twenty-two and reigned for half a century. His life was so completely identified with the government of the state that he offers less material for biography than his ancestor Abd-ar-Rahman I. Abd-ar-Rahman III was the grandson of his predecessor, Abdullah, one of the Spanish Umayyads.

Abd-ar-Rahman III came to the throne when the country was exhausted by more than a generation of tribal conflict among the Arabs, and of strife between them and the Muslims of native Spanish descent. Spaniards who were openly or secretly Christians had acted with the renegades. These elements, which formed the bulk of the population, were not averse from supporting a strong ruler who would protect them against the Arab aristocracy. These restless nobles were the most serious of Abd-ar-Rahman's enemies. Next to them came the Fatimids of Egypt and northern Africa, who claimed the caliphate based on descent from the Prophet Muhammad, and who aimed at extending their rule over the Muslim world. Abd-ar-rahman subdued the nobles by means of a mercenary army, which included Christians.

He repelled the Fatimids, partly by supporting their enemies in Africa, and partly by claiming the caliphate for himself. In the 10th century Abd-ar-rahman III declared the Caliphate of Cordoba, effectively breaking all ties with the Egyptian and Syrian Caliphs. His ancestors in Spain had been content with the title of sultan. The caliphate was thought only to belong to the prince who ruled over the sacred cities of Mecca and Medina. But the force of this tradition had been so far weakened that Abd-ar-Rahman could proclaim himself caliph on January 16, 929, and the assumption of the title gave him increased prestige with his subjects, both in Spain and Africa.

After he was defeated by the Christians at Alhandega in 939 through the treason of the Arab nobles in his army (see History of Spain) he never again took the field.