John Gresham Machen (July 28, 1881 – January 1, 1937) was an American Presbyterian theologian in the early 20th century. He was the Professor of New Testament at Princeton Seminary between 1915 and 1929, and led a conservative revolt against modernist theology at Princeton and formed Westminster Theological Seminary as a more orthodox alternative. As the Northern Presbyterian Church continued to reject conservative attempts to enforce faithfulness to the Westminster Confession, Machen led a small group of conservatives out of the church to form the Orthodox Presbyterian Church. When the northern Presbyterian church (PCUSA) rejected his arguments during the mid-1920s and decided to reorganize Princeton Seminary to create a moderate school, Machen took the lead in founding Westminster Seminary in Philadelphia (1929) where he taught New Testament until his death.