Biographies of great men are often undertaken by amateurs. Professional historians prefer to focus on collective institutions that are thought to be the theater of history properly understood. Geoffrey Parker has been a key figure in developing the “military revolution” hypothesis that has guided a good deal of recent work in early modern military history; he understands the perils of a biography better than most. But, having spent years amid the stacks of paperwork left by Spanish-Habsburg rulers, he also knows that the personal decisions of a Charles V (1500–58) made a difference. Charles signed more than 100,000 state documents, many of them with annotations in a distinctive hand that (one might say) only a mother could love.