Helmut Richard Niebuhr is considered one of the most important Christian theological ethicists in 20th-century America, best 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 the Yale Divinity School. Both brothers were, in their day, important figures in the neo-orthodox theological school within American Protestantism. His theology has been one of the main sources of postliberal theology, sometimes called the "Yale school". He influenced such figures as James Gustafson, Stanley Hauerwas, and Gordon Kaufman.