Alfonso VI of León and Castilla, was also king of Galicia and conquered the imperial city of Toledo. He also fought the battles of Sagrajas and Uclés, losing his first heir in the latter.
Although he was not the heir to the throne, since he was the second male child of the kings, his father decided to distribute his dominions among his five children, leaving León for Alfonso and Castilla to his first-born Sancho. However, Alfonso allied with Sancho to invade the kingdom of his younger brother, García, and they decided to divide the kingdom while they imprisoned him in Burgos.
Later both brothers got involved in a war from which he lost, but his brother decided not to pursue him, although later he was also taken prisoner in Burgos, to later transfer him to the Sahagún monastery, but his sister Urraca interceded for him and took refuge in the taifa of Toledo under the protection of one of its vassal kings. From there he formed an alliance with his sister Urraca and became strong in Zamora, a city besieged by his brother, during which he lost his life at the hands of an alleged traitor. After the death it was made again with Castile and Galicia.
After the murder of Sancho, distrust began between the Cid and the king, who tried to get closer to him by offering his niece Jimena and immunity in marriage, something that is currently doubted. García also took advantage of the death of his brother Sancho to claim his kingdom, but Alfonso called him to a meeting, in which he confined him in the castle of Luna where he would later die.
Once affirmed on his throne as Leon and under the title of emperor, he began to extend his dominions, defeating the Taifa kingdoms, exploiting his vassalage towards the Muslims. His ally in Toledo was poisoned and his grandson succeeded him, requesting help from the Leonese king. Alfonso took advantage of the moment to invade Toledo and take his king to Valencia under the protection of a noble ally. After the conquest of Toledo, he proclaimed himself emperor of the two religions, promising to reserve the main mosque for the Muslims of Toledo, although the archbishop revoked it taking advantage of the fact that the king was not there.
The pressure to which he subjected the Taifa kingdoms caused some of them to request help from the Almoravids, who sent troops to Extremadura in an attempt to free themselves from the Christian yoke.