Many founders of world religions didn't think of themselves as founders at all. They thought of themselves as radical reformers. Jesus thought he was transforming Judaism; Siddhartha Gautama said he was remaking Hinduism. And so it was with Martin Luther, who initially set out to revamp the Catholic Church but went on to launch the Reformation, which sparked the creation of Protestant Christianity. As we approach the 500th anniversary of this huge schism in church history on October 31st, we talk to the author of a book about a lesser-known era in Luther's life: his ten fearful yet productive months hiding out in a German castle. This segment first aired in 2015.