The words to Amazing Grace were written by John Newton, a former slave ship captain.
The film “Amazing Grace” is mostly the story of William Wilberforce’s work to abolish slavery throughout the British empire. It has some very good scenes between Newton & Wilberforce.
http://www.amazinggracemovie.com/
Here are a few quick wikipedia links:
http://en.wikipedia.org/wiki/John_Newton
http://en.wikipedia.org/wiki/Amazing_Grace
http://en.wikipedia.org/wiki/William_Wilberforce