Cacciato is an American soldier during the Vietnam War who decides to leave his squad and go AWOL. I think it can be argued that he represents control; specifically, the strict control and order wielded by the military structure. When he decides to desert, he undermines that control, and the men must hunt him down in order to reestablish the order and discipline they need to survive in battle.
Control is a central theme in the story. In his recollections, Paul is more naive than his comrades, and is not always sure about what he should do in a given situation. This indicates a lack of control on his part, a deficiency which is accentuated when, at a moment of crisis, he loses control of even his physical body and wets himself. The theme of control also extends to the larger war effort, and the need for absolute observance of military protocol on the part of an effective war machine. When that control is compromised, as evidenced in Sidney Martin's violation of standard operating procedure in searching the tunnels, chaos is bound to ensue.