Who is Callisthenes from The Campaigns of Alexander and what is their importance?

Callisthenes' friendship with Alexander ran afoul when Alexander claimed to be a living god and required those in his presence to prostrate themselves. Callisthenes argued against his claim, citing that living people could not be gods, because gods are not of the earth. After people die they might become gods though, and this was the whole point of Callisthenes' argument. Alexander took great offense at his claims and later implicated Callisthenes in a plot to kill him. Thus, he felt justified in killing Callisthenes.