The lyrics to "Amazing Grace" were written by John Newton (1725-1807). He was born in London, England and began sailing with his father at a young age.  Newton spent part of his early adulthood as a slave trader before eventually deciding to devote his life to the church and to support abolition (a movement to end slavery).  

When Newton became a clergyman (a leader in the church) he wrote about a frightening storm he sailed through and the "grace" he received to have survive that scary night.  The song's melody is believed to have come from African slaves as a chant of sorrow.  "Amazing Grace" is very famous and believed to be performed over 10 million times a year in church services, funerals and stages everywhere .