Helmut Richard Niebuhr was one of the most important Christian theological-ethicists in 20th century America, most known for his 1951 book Christ and Culture and his posthumously published book The Responsible Self. The younger brother of theologian Reinhold Niebuhr, Richard Niebuhr taught for several decades at Yale Divinity School. His theology (together with that of his colleague at Yale, Hans Wilhelm Frei) has been one of the main sources of post-liberal theology, sometimes called the "Yale school". He influenced such figures as James Gustafson and Stanley Hauerwas.