Fernando I of León

Ferdinand I
Ferdinand (left) and his wife Sancha, from an illumination in a contemporary manuscript.
Emperor of all Spain
Reign	1056–1065
Coronation	c. 1056
Predecessor	Vacant Bermudo III
Successor	Vacant Alfonso VI
King of León and Castile
Reign	1037–1065
Coronation	22 June 1038 (León)
Predecessor	Bermudo III (in León)
Successor	Sancho II (Castile), Alfonso VI (León) and García II (Galicia)
Count of Castile
Reign	1029–1037
Predecessor	García Sánchez
Successor	title in abeyance
Born	c. 1015
Died	24 December 1065 (aged 49–50) León
Burial	Basilica of San Isidoro
Consort	Sancha of León
Issue	Urraca of Zamora Sancho II Elvira of Toro Alfonso VI García II
Dynasty	Jiménez
Father	Sancho III of Navarre
Mother	Muniadona of Castile
Religion	Roman Catholicism

Ferdinand I (c. 1015 – 24 December 1065), called the Great (el Magno), was the Count of Castile from his uncle's death in 1029 and the King of León after defeating his brother-in-law in 1037. According to tradition, he was the first to have himself crowned Emperor of Spain (1056), and his heirs carried on the tradition. He was a younger son of Sancho III of Navarre and Muniadona of Castile, and by his father's will recognised the supremacy of his eldest brother, García Sánchez III of Navarre. While Ferdinand inaugurated the rule of the Navarrese Jiménez dynasty over western Spain, his rise to preeminence among the Christian rulers of the peninsula shifted the locus of power and culture westward after more than a century of Leonese decline. Nevertheless, "[t]he internal consolidation of the realm of León–Castilla under Fernando el Magno and [his queen] Sancha (1037–1065) is a history that remains to be researched and written."

There is some disagreement concerning the order of birth of Sancho III's sons, and of Ferdinand's place among them. He was certainly a younger son, and he was probably born later than 1011, by which date his parents are known to have married. Most, and the most reliable, charters name Sancho's sons in the order Ramiro, García, Gonzalo, then Ferdinand. Three documents from the Cathedral of Pamplona list them in this way, as well as four from the monastery of San Juan de la Peña. One charter from Pamplona, dated 29 September 1023, is witnessed by Sancho's mother, Jimena Fernández, his wife Muniadona, her children, listed García, Ferdinand then Gonzalo, and their brother, the illegitimate Ramiro.