"Amazing Grace" is a song about the joy of discovering God's love and realizing you have been saved. It's served as a rallying cry for people in desperate need of spiritual support for centuries due to the pure joy its lyrics convey. And yet few people know that the man who wrote those lyrics spent much of his early life an unrepentant sinner—and a slave trader.
Biography explains that the song was written by John Newton. Born in 1725, Newton lost his mother when he was very young, and was raised by his sea-captain father, who frequently took Newton on voyages with him. Newton grew into a reckless young man who drank too much and got into a lot of trouble. Christianity Today reports that Newton lost jobs due to his "unsettled behavior," and was eventually pressed into the British Navy—but deserted. Later, he managed to get himself transferred to a slaver ship transporting human beings to bondage.
Newton experienced a near-death experience during one of his voyages and converted to Christianity as a result. For years this renewed faith was mostly talk as Newton continued to live a sordid life, but slowly he came to regret his ways, especially his involvement with slavery. Retiring from the sea, he became an ordained minister in 1764.