The King of León was a title held by the rulers of the medieval kingdom of León in the northwest of the Iberian Peninsula. Established in the 10th century, León became a significant political and cultural center during the Reconquista, a period marked by the Christian kingdoms' efforts to reclaim territory from Muslim rule. The kingdom played a crucial role in the formation of modern Spain. The most notable monarchs included Ferdinand I, who united León with Castile, and Alfonso VI, known for his military conquests and cultural patronage. The kingdom eventually merged with Castile in the 13th century, leading to the rise of the unified Spanish crown.