Peter Shaffer based The Royal Hunt of the Sun on William H. Prescott's History of the Conquest of Peru. He made few substantive changes, since Prescott's account is already full of drama, but one important alteration lies in the character of Pizarro and his treatment of Atahualpa. Prescott sees Pizarro's conduct as disgraceful, whereas Shaffer treats him with greater sympathy. It would have been easy to make Pizarro a straightforward villain and therefore render the lessons taught by the play entirely negative, but Shaffer's message is more complex.

The lessons that the play teaches about greed, trust, honor, and a host of other qualities is that they are all finite and contingent. Pizarro is, by his own standards, a fairly honorable man, but he is continually forced to make compromises, particularly with the men he theoretically leads. Atahualpa and Pizarro come to trust one another, but only up to a point. They cannot place infinite trust even in themselves and the religious beliefs they hold. Even greed is finite, demanding just enough gold to fill a room.

These points may seem rather obvious, but they are valuable lessons for an age that has come to believe in binary oppositions and simplistic motives. Shaffer reminds his audience that the world is not divided into the greedy and the disinterested or the honorable and the treacherous. All qualities are present in all people to some degree, and none are infinite in anyone.