Paul Johannes Tillich (August 20, 1886 – October 22, 1965) was a German-American Christian existentialist philosopher, religious socialist, and Lutheran Protestant theologian who is widely regarded as one of the most influential theologians of the twentieth century. Tillich taught at a number of universities in Germany before immigrating to the United States in 1933, where he taught at Union Theological Seminary, Harvard Divinity School, and the University of Chicago.