The Poem of the Cid recounts the fictionalized adventures of Rodrigo Diaz, an eleventh-century Castillian who conquered much of Islamic Spain. Many of the events in the poem are historically accurate, but licenses have been taken by the poet, generally to allow more opportunities for the Cid to prove his valor and loyalty to King Alfonso. In fact, throughout the entire poem, the Cid is portrayed as an exemplary hero and vassal; he is also an ideal lord himself. The poet has created an ideal within the historical context of eleventh- or twelfth- century Spain. .
The Cid is exiled because his enemies have turned King Alfonso against him. This, according to custom, gives Rodrigo the right to earn a living for himself and his followers, to claim authority over whatever territory he conquers, and even to wage war against his former lord. Essentially, by exiling him, Alfonso has relieved him of his obligations as a vassal. .
These obligations revolve around fidelity, loyalty, and support. The Cid continues to act as a superbly successful vassal, sending Alfonso rich spoils from his conquered territories and humbling himself through his messengers. When restored to the king's favor, he defers to Alfonso's wishes, even when they conflict with his own, as in the case of his daughters' marriages. Central to the feudal system is the fact that vassals of a lord often have vassals themselves. The Cid is presented as being an ideal lord as well, which seems to balance the humility he shows to Alfonso. He is generous to his followers, shows them respect, and accepts their counsel. Perhaps most importantly, he allows his vassals to serve him honorably. He often sends Minaya as a messenger, and the latter fulfills his duty much as Rodrigo obliges Alfonso. At the trial of the heirs of Carrion, who have dishonored and injured the Cid's daughters, the Cid suggests that his vassals offer a challenge, implying that they should fight for his honor.