King Alfonso XI of Castile was a monarch who ruled from 1312 to 1350. He was the son of King Ferdinand IV and Queen Constance of Portugal. Alfonso is known for his military campaigns against the Moors in the Iberian Peninsula, which helped to expand the territory of Castile. Alfonso XI implemented significant administrative reforms and promoted the use of the Spanish language in official documents. His reign also saw the establishment of the Order of the Knights of Santiago, which played a crucial role in the Reconquista. He died during the Black Death, leaving a legacy of both military and cultural achievements.