Das Spiel Azad by Iain Banks

A masterful gamesman from an advanced, post-scarcity civilization, bored with success and searching for challenge, is recruited to compete in a vast, ritualized tournament whose rules determine the political rank and fate of an authoritarian alien empire; as he rises through ever more elaborate stages, the contest becomes a mirror for questions of power, culture and morality, exposing how a society’s structures are encoded into its games and forcing difficult choices about intervention, identity and the costs of victory.