John Henry Gerstner (1914–1996) was an American preacher, theologian, and professor whose ministry and scholarship significantly influenced 20th-century Reformed evangelicalism. Born in Tampa, Florida, he spent his childhood in Philadelphia, where he graduated from high school in 1932. That summer, while visiting Philadelphia College of the Bible, he experienced a profound conversion to Christianity, setting the course for his life’s work. Gerstner pursued extensive education, earning a BA from Westminster College, a Master of Divinity and Master of Theology from Westminster Theological Seminary, and a PhD in Church History from Harvard University in 1945. Ordained in the United Presbyterian Church of North America, he later served in the Presbyterian Church (USA) before joining the Presbyterian Church in America in 1990, reflecting his commitment to conservative theology. He married Edna Suckau, with whom he had three children. Gerstner’s preaching career intertwined with his academic roles, most notably as professor of Church History at Pittsburgh Theological Seminary (1950–1980) and Knox Theological Seminary, where he was an authority on Jonathan Edwards. Known for his rigorous intellect and Socratic teaching style, he mentored influential figures like R.C. Sproul, founder of Ligonier Ministries, through which his sermons and lectures reached a broader audience. His preaching emphasized biblical inerrancy, Reformed theology, and Edwards’s evangelistic fervor, themes echoed in over 20 books, including The Rational Biblical Theology of Jonathan Edwards and Primitive Theology. Gerstner died in 1996 in Ligonier, Pennsylvania, leaving a legacy as a defender of orthodox faith, celebrated for his clarity, piety, and dedication to equipping the church with sound doctrine.