J. Gresham Machen (1881-1937) was an American theologian and New Testament scholar known for his strong defense of orthodox Christianity. He was a professor at Princeton Theological Seminary and later founded the Orthodox Presbyterian Church in response to modernist theology, which he believed undermined traditional Christian beliefs. Machen authored several influential works, including Christianity and Liberalism, where he argued that liberal Christianity was fundamentally different from historic Christianity. His commitment to the authority of Scripture and the importance of doctrinal purity made him a significant figure in the early 20th-century conservative Christian movement.