Could you please tell me what a Hegemon is?
The word, which is of Greek origin, is used slightly differently in Ender's Game. The term "hegemony" in modern usage means the supremacy of one nation over others -- dominance but not necessarily imperial control. So in the Ender's Game future, when the nations wanted to create an authority more binding than the United Nations while preserving national autonomy in matters not concerned with building and deploying, staffing and paying for the international fleet, they created the office of "hegemon" to exercise hegemony over all the nations. His authority is balanced by the independent offices of Polemarch and Strategos, commanding the fleet and the troops, respectively. Since they are independently appointed, the hegemon does not control them; but since the hegemon funds them, they still are accountable to him, and he to them, to some degree.