Seventeen : last man standing
(Book)

Behind the events you know are the killers you don't. When diplomacy fails, we're the ones who gear up. Officially we don't exist, but every government in the world uses our services. We've been saving the world, and you, for one hundred years. Sixteen people have done this job before me. I am Seventeen. The most feared assassin in the world. But to be the best, you must beat the best. My next target is Sixteen, just as one day Eighteen will hunt me down. It's a dog-eat-dog world and it gets lonely at the top. Nobody gets to stay for long. But while we're here, all that matters is that we win.