As soon as he took the throne, he began working hard to strengthen royal power by dividing his enemies. His early display of rulership skills included the unhesitant execution of possible opponents (Don Juan el Tuerto in 1326, among others). He managed to extend the limits of his kingdom to the Strait of Gibraltar after the important victory at the Battle of Salado against the Marinid Dynasty en 1340 and the conquest of the Kingdom of Algeciras in 1344. Once that conflict was resolved, he redirected all his Reconquista efforts to fighting the Moorish king of Granada. He is variously known among Castilian kings as the Avenger or the Implacable, and as "He of Rio Salado." The first two names he earned by the ferocity with which he repressed the disorders caused by the nobles during his long minority; the third by his victory in the Battle of Rio Salado over the last formidable Marinid invasion of Iberian Peninsula in 1340. Alfonso XI never went to the insane lengths of his son Peter of Castile, but he could be bloody in his methods. He killed for reasons of state without any form of trial. He openly neglected his wife, Maria of Portugal, and indulged a scandalous passion for Eleanor of Guzman, who bore him ten children. This set Peter an example which he failed to better. It may be that his early death, during the Great Plague of 1350, at the Siege of Gibraltar, only averted a desperate struggle with Peter, though it was a misfortune in that it removed a ruler of eminent capacity, who understood his subjects well enough not to go too far.

She was born on 9 February 1313. Maria became Queen consort of Castile upon her marriage to Alfonso XI in 1328. She was the mother of Pedro of Castile. The relationship between Maria and Alfonso was unhappy: from 1327 before their marriage, Alfonso had a relationship with Leonor Núñez de Guzmán. In 1335, Maria returned to her father in Évora, who demanded that Alfonso separated from Leonor by use of alliances with the Pope, the Muslims and rebels inside Castile, and finally by an invasion. In the peace treaty of Seville in July 1340, Alfonso agreed to have Leonor imprisoned in a convent. At the death of Alfonso 26 March 1350, Maria secured a power position by exerting influence upon the leader of her son's council, Juan Alfonso de Alburquerque. She participated in the rebellion against her son in 1354, and turned over Toro to the rebels, which caused his imprisonment. After this, she returned to Portugal.