“Ranimirus proles regis, Garseanes frater eius, Gundisaluus frater eius, Ferdinandus frater eius” confirmed the charter dated 17 Apr 1014 under which “Sancius…rex…cum coniuge mea regina domina Maiora” donated property to the monastery of Leire, although the absence of the brother Bernardo suggests that this charter should be redated to approximately ten years later. "Sancius…rex" recommended the rule of St Benedict to the monastery of Leire by charter dated 21 Oct 1022, subscribed by "Eximina regina mater regis, Regina domna Muma, Garsia et Ranimirus, Gundesalbus et Fernandus". The charter of "Sancius Hispaniarum rex" dated 26 Jun 1033 relating to concessions to the monastery of Oriense was confirmed by his sons (in order) "Ranimirus…Garsea…Fredinandus". His father installed him as Conde de Castilla in 1029, in succession to his maternal uncle. The Historia Silense records that King Sancho granted "Castella" to "Fernandum".
Under the division of territories organised by his father prior to his death, he received Castile, succeeding in 1035 as FERNANDO I "el Magno" King of Castile. With the help of his brother García V King of Navarre, he defeated and killed his brother-in-law Vermudo III King of León, proclaiming himself King of León and Galicia 4 Sep 1037. Crowned at Santa María de León 22 Jun 1038, after which he used the title "imperatur". Ferdinand I King of Castile confirmed the union of the monastery of San Martín del Río with San Pedro de Cardeñas by charter dated 31 Aug 1050, subscribed by "Sanctius prolis regis, Adefonsus filius regis, Garsea filio regis, Urraca filia regis, Tegridia filia regis…". King Fernando's reign was a period of rapid Castilian expansion. He defeated and killed his brother García Sánchez III King of Navarre at Atapuerca Sep 1054, requiring the cession of the Bureba district on the west bank of the upper Ebro River. The close ties between Burgundy and Spain started during the reign of Fernando I King of Castile, who established an annual rent of 120 ounces of gold in favour of the Abbey of Cluny some time after 1055. He allied himself with Ibn-Hud to attack the Taifa Kingdom of Toledo, from whom he forced the payment of a large tribute or paria, which became the established way of raising revenues for the Christian kingdoms. In 1057, he invaded the territory of the Aftasids of Badajoz, capturing Lamego 29 Nov 1057 and Viseu 25 Jul 1058. He also attacked Santarem, forcing its ruler to pay 5,000 dinars a year to maintain a truce. He exacted annual parias from Zaragoza from 1060. King Fernando donated property "in Compostella…[qui] fuit…de Odrozia comitssa…cum filia sua Gyloira et…nepus suum comitem Monninum Ruderici" to Celanova by charter dated 19 Aug 1061. He conquered Coimbra after a 6 month siege ending 25 Jul 1064. He also reclaimed much of the traditional Castilian territory held by Sancho IV García King of Navarre, but this was apparently a political and diplomatic rather than a military process. A great council meeting in 1064 agreed a division of King Fernando's territories (as well as the rights to annual parias from the Taifa kingdoms) between his sons, the agreement being implemented after his death. The precise geographical details of the split are set out by Reilly and in the Chronicon Regum Legionensium. "Fredernandus…Legionensis rex…cum coniuge mea regina dna Sancia et filiis meis" confirmed the privileges of Santiago de Compostela by charter dated 10 Mar 1065, subscribed by "Sancius filius regis, Adefonsus filius regis, Garsea filius regis, Urraca filia regis, Geloira filia regis…".
The Chronicon Regum Legionensium records the death of Fernando I King of Castile "in the era 1103 (1065)" after reigning for 18 years and his burial with his wife Sancha "in the city of León". The Chronicon Lusitanum records the death of “Rex Domnus Fernandus” in 1103 (adjusted to 1065) and his burial “VII Kal Jan…in Legionensi civitate”. The Chronicon Burgense records the death “in die S. Eugeniæ” in 1065 of “Fernandus Rex”. The Chronicon Regum Legionensium records the death of Fernando I King of Castile "in the era 1103 (1065)" after reigning for 18 years and his burial with his wife Sancha "in the city of León". 1