Amazing Grace is a 2006 film starring Ioan Gruffudd as William Wilberforce, a wealthy politician and reformer. After a religious conversion, Wilberforce considered becoming part of the clergy, but was encouraged to continue to serve God as a politician. While the film does contain a few historical inaccuracies (for instance, he sings Amazing Grace several years before the tune was added to the lyrics), it is a very well made movie that captures the heart and spirit of Wilberforce and the causes he championed.
Frankly, it is one of my favorite films from this century and one I watch several times a year. The emphasis on his relationship God and his belief in treating all humans (and animals; Wilberforce was also a founding member of the Royal Society for the Prevention of Cruelty to Animals) with kindness and respect are done quite well. I highly recommend this film!