Ferdinand I or Ferdinand the Great, d. 1065, Spanish king of Castile (1035–65) and León (1037–65). He inherited Castile from his father, Sancho III of Navarre, conquered León, and took parts of Navarre from his brother García. Ferdinand fought successfully against the Moors and reduced to vassalage the Moorish kings of Zaragoza, Badajoz, Seville, and Toledo. At the Council of Coyanza (1050) he confirmed the laws of Alfonso V and introduced church reforms. He divided his kingdom among his sons: Castile went to Sancho II, León to Alfonso VI, and Galicia to García.
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