Dietrich Bonhoeffer was an extraordinary man who came from a very prominent and proud German family. His intellect, experiences, and disciplines strengthened his faith in such a way that he was a shining light to Jews and oppressed Germans who were under the Third Reich's Nazi Regime. His involvement in the resistance as a Pastor is a remarkable story and is pulled together nicely in Bonhoeffer: Pastor, Martyr, Prophet, Spy by Eric Mataxas. Although Mataxas has received some very critical reviews, especially pertaining to his research, I still found this biography very enlightening and enjoyable to read.
Having recently finished a biography on Dwight Eisenhower, it was interesting to see WWII from the perspective of the Allies and a German. This book gives you a greater appreciation of the German people who were oppressed, while also giving you an even greater distaste for those deeply involved in the S.S. The biography also will give you better insight and more appreciation of Bonhoeffer's other works, particularly The Cost of Discipleship.
If you are going to read a biography soon, this is a good one. Bonhoeffer's story will challenge you in your faith and stretch you beyond a way of life that can easily become all too comfortable within the States.