John Gresham Machen (1881–1937) was a prominent American preacher, scholar, and theologian, widely regarded as a leading defender of orthodox Presbyterianism in the early 20th century. Born in Baltimore, Maryland, to a well-to-do family, Machen grew up in a devout Presbyterian household shaped by his mother’s Southern Presbyterian roots and his father’s legal career. He excelled academically, earning degrees from Johns Hopkins University, Princeton University, and Princeton Theological Seminary, and pursued further studies in Germany under liberal theologians, which sharpened his conservative convictions. Ordained in 1914, he joined the faculty of Princeton Seminary, where he taught New Testament from 1906 until 1929, emerging as a staunch opponent of theological liberalism infiltrating mainline Protestantism. Machen’s ministry reached a turning point amid the fundamentalist-modernist controversy. In 1929, he left Princeton Seminary due to its growing liberal shift, founding Westminster Theological Seminary in Philadelphia to preserve rigorous, confessional training. His book Christianity and Liberalism (1923) argued that liberalism was a different religion from historic Christianity, cementing his reputation as a scholarly firebrand. In 1933, he established the Independent Board for Presbyterian Foreign Missions, leading to his 1936 defrocking by the Presbyterian Church (USA) for defying denominational authority. Undeterred, he helped form the Orthodox Presbyterian Church in 1936. Machen died of pneumonia in 1937 while preaching in North Dakota, leaving a legacy as a brilliant apologist and uncompromising advocate for biblical orthodoxy.