Possibly fathered by Adam's half-brother, Charles, Caleb is possibly Aron's half brother. He is very much Aron's opposite. "Cal was growing up dark-skinned, dark-haired. He was quick and sure and secret. Even though he may have tried, he could not conceal his cleverness. Adults were impressed with what seemed to them a precocious maturity, and they were a little frightened at it too. No one liked Cal very much and yet everyone was touched with fear of him and through fear with respect. Although he had no friends he was welcomed by his obsequious classmates and took up a natural and cold position of leadership in the schoolyard." Jealous of his more likeable brother, Cal is manipulative and brutal; yet he struggles with his dark side, haunted by the thought that he may have inherited his mother's evil. As a Cain figure, he unwittingly kills his brother by revealing their mother's unsavory identity—a prostitute: abysmally distraught, Adam joins the army only to meet with his death in World War I. At the end of the book, he is blessed by his father with the all-important principle of timshel, "thou mayest": free will, the capacity to choose how you will live your live, given the struggle between good and evil within and without.