October 2017 marks five hundred years since Martin Luther nailed his 95 theses to the church door in Wittenberg and launched the Protestant Reformation. At least, that's what the legend says. But with a figure like Martin Luther, who looms so large in the historical imagination, it's hard to separate the legend from the life, or even sometimes to separate assorted legends from each other. Over the centuries, Luther the man has given way to Luther...