Dietrich Bonhoeffer Pursuing Costly Grace

Dietrich Bonhoeffer ( 4 February 1906 – 9 April 1945) was a German pastor, theologian, spy, anti-Nazi dissident, and key founding member of the Confessing Church. His writings on Christianity's role in the secular world have become widely influential, and his book The Cost of Discipleship has become a modern classic.

Apart from his theological writings, Bonhoeffer was known for his staunch resistance to Nazi dictatorship, including vocal opposition to Hitler's euthanasia program and genocidal persecution of the Jews. He was arrested in April 1943 by the Gestapo and imprisoned at Tegel prison for one and a half years. Later he was transferred to a Nazi concentration camp. After being associated with the plot to assassinate Adolf Hitler, he was quickly tried, along with other accused plotters, including former members of the Abwehr (the German Military Intelligence Office), and then executed by hanging on 9 April 1945 as the Nazi regime was collapsing.
https://en.wikipedia.org/wiki/Dietrich_Bonhoeffer

Bonhoeffer was teaching pastors in an underground seminary, Finkenwalde (the government had banned him from teaching openly). But after the seminary was discovered and closed, the Confessing Church became increasingly reluctant to speak out against Hitler, and moral opposition proved increasingly ineffective, so Bonhoeffer began to change his strategy. To this point he had been a pacifist, and he had tried to oppose the Nazis through religious action and moral persuasion.

Now he signed up with the German secret service (to serve as a double agent—while traveling to church conferences over Europe, he was supposed to be collecting information about the places he visited, but he was, instead, trying to help Jews escape Nazi oppression). Bonhoeffer also became a part of a plot to overthrow, and later to assassinate, Hitler.
http://www.christianitytoday.com/history/people/martyrs/dietrich-bonhoeffer.html