Dubbed at his death "Doctor Fundamentalis," J. Gresham Machen (1881-1937) was one of the most significant defenders of evangelical Christianity in the early twentieth century. Raised in American Presbyterianism, he wrestled deeply with the challenge of Protestant Modernism and provided some of the most significant responses to it, particularly his classic book Christianity and Liberalism. He pointed the way forward toward a Christianity that was both intellectually rigorous and spiritually satisfying, one that was rooted in a trustworthy Bible and in a confessional tradition which in turn produced a genuine faith in Christ. As a result, Machen continues to provide lessons today for those who desire to be valiant for truth in the midst of a hostile world.