Mercenary — Jerry Pournelle

WHY HAS JOHN CHRISTIAN FALKENBERG THROWN MILLIONS OF PEOPLE ON DOZENS OF PLANETS INTO TURMOIL?

Because he's given up the brilliant military career he's known since age fifteen to fight on his own.

Because he's a legend to the Earth-bound, a mastermind to his soldiers, an enigma to the politicians who buy his services.

But mostly because he's John Christian Falkenberg.