Surface Detail by Iain M. BanksTHIS
If you haven't read "Player of Games" by the same author, then we need to reevaluate our relationship. He writes a novel about a multi-system empire where the dominant species has three genders (very well executed) and the leader of the empire is the winner of a tournament. (They play a chess like turn based strategy game. It's real, as in board game / card game hybrid, and you can bet on it up to and including your genitals. Loser will have theirs cut off.) The libertarian/anarchist galactic culture, known as "The Culture" sends its own representative to enter the tournament, with the goal of becoming Emperor and dismantling the empire.
Did I mention that you should read it.