The Chronicon Regum Legionensium names (in order) "Urraca, Sancho, Alfonso, García and Elvira" and the children of King Fernando and Queen Sancha. According to the Chronicle of Sahagún, Alfonso was 72 years old when he died, but this must be overstated if he was his parents' fourth child as stated in Historia Silense. It is more likely that he was born in [1038/40]. 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…". "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…".
Under the partition of lands in his father’s will, he received León and the parias from the Taifa state of Toledo, succeeding in 1065 as ALFONSO VI King of León.
Betrothed (by proxy Caen, Abbey of Holy Trinity before ) to Agathe de Normandie, daughter of William I King of England Duc de Normandie & his wife Mathilde de Flandres... According to William of Malmesbury, an unnamed daughter of King William was "affianced by messengers" to King Alfonso. Orderic Vitalis names her Agatha, identifying her as the daughter who had been betrothed to Harold Godwinson... and says that she was betrothed to "Amfursio regi Galliciæ". Matthew of Paris places her as the fifth daughter (unnamed) betrothed to "Aldefonso Galiciæ regi" but different from the daughter betrothed to Harold. Orderic says that she died en route to Spain, her body being brought back to Bayeux for burial. The betrothal to Alfonso must have been a short-lived arrangement as he married his first wife in 1069.
Relations between Alfonso and his two brothers were tense. Although Alfonso and Sancho cooperated to deprive their brother García of Galicia, Sancho turned against Alfonso soon afterwards and defeated him at Golpejera Jan 1072. He was exiled to Toledo, seeking refuge with the Dhul-Nunid King. He returned to León after the murder of his brother, arriving  Nov 1072, and was accepted before 8 Dec 1072 as ALFONSO VI King of Castile. Pursuing his father's close connections with the monastery of Cluny, he granted the order its first monastic house in Castile at San Isidro de Dueñas 29 May 1073, as well as doubling the annual census payment to Cluny in 1077. The Roman liturgy was adopted in Castile and León in 1076. After the death in Jun 1076 of Sancho IV “él de Peñalén” King of Navarre, King Alfonso succeeded as King of Navarre: a charter dated 1076 records that Alfonso VI King of Castile ("Adefonsus filius Fredinandi regis") succeeded to the kingdom after "impiisima fraude interfecto rege Sancio, Garsie...regis filius". Pope Gregory VII asserted papal suzerainty over Spain 28 Jun 1077, although King Alfonso's response appears to have been to declare himself "imperator totius hispaniae", the first known use of this title being 17 Oct 1077. King Alfonso VI took advantage of the assassination of Sancho IV King of Navarre in 1076 to invade Navarre, annexing La Rioja, Álava, Vizcaya and Guipúzcoa to Castile. Turning his attention to the reconquest of Moorish territories, Alfonso recaptured Toledo 25 May 1085, besieged Zaragoza in 1086, and also imposed his Government on the kingdom of Valencia, where he installed as ruler the deposed al-Qadir ex-taifa King of Toledo. His ambitions were, however, thwarted by al-Mu'tamid King of Seville who, with the help of Yusuf bin Tashfin Emir of the Almoravids, defeated King Alfonso at Sagrajas near Badajoz 23 Oct 1086. The Almoravids rapidly consolidated their position, absorbing the taifa kingdoms of Granada and Seville and subduing Jaén, Almería, Denia and Murcia. Undeterred, Alfonso recaptured Córdoba in 1091, and persuade Al-Mutawakkil of Badajoz to cede him Lisbon, Santarem and Sintra between 30 Apr and 8 May 1093, although Badajoz itself was captured by the Almoravids in early 1094. Meanwhile Rodrigo Díaz "el Cid" recaptured Valencia, establishing himself there as an autonomous prince. Previously his bitter enemy, Alfonso eventually united with him to fight the Moors. He also spread the call overseas, especially in France, for a general crusade to fight 'the infidel'.
"Adefonsus rex Legionis et totius Hispanie imperator atque Fredenandi filius regis" granted privileges to Santiago de Compostela, with the advice of "generis mei comitis domini Raimundi", by charter dated 28 Jan 1090. The end of his reign was marred by a crushing defeat at Uclés 29 May 1108, where his son was killed. The Chronicon Regum Legionensium records that King Alfonso lived for 79 years and reigned for 43 years and six months, died in Toledo 1 Jul "in the era 1147 (1109)" and was buried "in the church of saints Facundus and Primitivus". The Chronicon Lusitanum records the death “III Kal Jul” in 1147 (1109) of “Rex D. Alfonsus Regis D. Fernandi filius”. 1
Alfonso married Agnes D' AQUITANE, daughter of Guillaume VIII D' AQUITAINE, Comte de Poitou, and Mathilde, about 1073. Alfonso repudiated Agnes after 22 May 1077. (Agnes D' AQUITANE was born about 1059 and died on 6 Jun 1078.).
Alfonso also married Constance CAPET de Bourgogne, daughter of Robert I "Le Vieux" CAPET, Duc de Bourgogne, and Ctse Hélie DE SEMUR-EN-AUXOIS, in Dec 1079. (Constance CAPET de Bourgogne was born about 1046 in Bourgogne, Marne, France and died between 3 Apr 1093 and 25 Oct 1093.
Alfonso also married Berta DE BOURGOGNE, possibly daughter of Cte Guillaume I "le Grand" DE BOURGOGNE and Étiennette, in Dec 1094. (Berta DE BOURGOGNE died in Jan 1100.
Alfonso also married Isabel (Elisabeth) before 14 May 1100 in Burgos, Castile. (Isabel/Elisabeth died before Mar 1106.)
Alfonso also married Zaïda, widow of Abu Nasir al Fatah al Ma'Mun, Emir of Córdoba, in Mar 1106. Zaïda was born about 1071 and died on 13 Sep 1107 in Spain.)
Alfonso also married Beatrix about Apr 1108. (Beatrix died after 1109.)