Paul Tillich was a German-American theologian and philosopher, known for his influential work in the fields of theology, existentialism, and philosophy of religion. Born in 1886, he became a prominent figure in 20th-century thought, integrating ideas from psychology, sociology, and philosophy into his theological framework. His most notable concepts include the "courage to be" and the idea of God as the "ground of being." Tillich's writings often explored the relationship between faith and culture, emphasizing the importance of addressing existential questions. He taught at several institutions, including Union Theological Seminary and Harvard University, and his works continue to inspire discussions in theology and philosophy today.