Excerpts from Books and Wikipedia
"Ferdinand died in December 1065, and by the turn of the new year his kingdom was once again divided, by the terms of his will and by the resulting fratricidal struggles among his three sons. Ferdinand left his kingdom split so that Sancho, his oldest son, inherited Castile itself; Alfonso, apparently his father’s favorite, got the kingdom of Leon, a considerably richer prize; and the youngest, Garcia, was allotted the farthest and poorest corner, Galicia. There was yet another key player in this nearly Shakespearean chain of quarrels among the brothers that began in 1066 and continued all the way into Toledo in 1085: a man named Rodrigo Diaz, one of the most prominent warriors and courtiers in the service of Sancho, the oldest of the brothers. Rodrigo Diaz would be remembered far and wide and across history as the Cid . . . An embattled Toledo, coveted by other taifas—but especially by archrival Seville—thus came under Alfonso’s protection . . . This was an eventful decade, during which Alfonso continued to expand his territories and consolidate his holdings. These were also years during which Rodrigo Diaz established his reputation as a warrior and earned his honorific 'Cid.'”