Dietrich Bonhoeffer was a German theologian in the first half of the 20th century, the author of the influential theological works The Cost of Discipleship and Life Together. Bonhoeffer was a leading theological voice in the debates between liberal theology, neo-orthodoxy, and fundamentalism during his lifetime. His contributions—particularly in their ethical and pastoral applications—have attracted a wide Christian readership. Many of his theological insights are centered on the nature of the church; his emphasis on the importance of church fellowship challenged the individualistic tendencies of some versions of Protestant Christian practice.

Bonhoeffer came from an educated family, with a father who worked as a notable psychologist and a brother who was a nuclear physicist. Bonhoeffer received a robust education and developed a particular aptitude for philosophy, logic, and music, while his mother influenced the development of his Christian faith. He was personable and quick to make friends, but also given to periods of deep reflection and even, at times, depression. He studied theology at the University of Berlin, gaining a doctorate and also writing a postdoctoral thesis. While he remained active in academics and taught courses from time to time, much of his early career was spent in pastoral ministry.