Who is Captain Ariostos from City of the Beasts and what is their importance?

Captain Ariostos is the military leader, who is in charge of a group of soldiers traveling with the International Geographic team. In reality, however, he is really in league with Carias and planning to exterminate the natives of the region. Ariostos is to be paid by Carias for his efforts and expects to be ready to retire soon after the expedition.