39. John Newton and David Brainerd

The former slave trader turned Christian preacher left his most famous and enduring legacy in the beloved hymn, Amazing Grace. John Newton's life was, however, complex and troubled, with many pressures and challenges impeding his progress from a slaver to one of England's most famous and influential abolitionists. At the same time, in America, the young David Brainerd brought the message of the gospel to native tribes along the colonial frontier, and although he died at a very young age, his life left an impact that would inspire the sweeping effort known as the modern missionary movement.