Cur Deus Homo was written in the late eleventh century by St. Anselm, archbishop of Canterbury. Anselm was a Benedictine monk, and he rose through the ranks of the Benedictine order and became an abbot of his own monastery in Bec (in modern France). This gave him significant power within the power structure of the Middle Ages, and in fact Bec became a renewed center of learning largely as a result of Augustine's influence. Insofar as this is a theological treatise, it does not include characters such as appear in the novel, but rather religious figures. Those most discussed herein are Adam and Eve, Jesus, the devil, and the infidels.

Adam and Eve are the prototypical humans, and those responsible for original sin (though many of the human race sin daily since then). Had Adam not sinned, according to Anselm, God would have transported mankind into a state of immortal existence. Anselm focuses heavily on Adam as the specific race from which God needed to exact atonement. If God created another race, Adam's specific race would not have an opportunity to be redeemed. Eve is Adam's female counterpart, and from this pairing everyone in the race of man descended.

Jesus Christ, whom God made so that Jesus could delight in the enjoyment of God, is made in two images: the human and the divine. According to Anselm, he is one person of two natures. Anselm's central argument in Cur Deus Homo is that only a man (of Adams's race) could successfully atone for mankind's sins, but this individual must, too, share in God's divinity, else the atonement would be insufficient recompense for man's sin.

Anselm describes the devil as being unjust rather than just (like God). The devil is responsible for mankind's sins, both for temping man and imparting violent nature to man. God had justice his side in striving against the devil for the liberation of man.

Finally, Anselm frequently makes mention of "the infidels" as individuals who question the nature of Jesus Christ and the logic behind God's incarnation as Jesus, a man. When he refers to this group, he is addressing primarily Jews and Muslims.