Timothy James Keller was an American Calvinist pastor, preacher, theologian, and Christian apologist. He was the chairman and co-founder of Redeemer City to City, which trains pastors for service around the world. He was also the founding pastor of Redeemer Presbyterian Church in New York City and the author of The New York Times bestselling books The Prodigal God: Recovering the Heart of the Christian Faith (2008), Prayer: Experiencing Awe and Intimacy with God (2014), and The Reason for God: Belief in an Age of Skepticism (2008). The prequel for the latter is Making Sense of GOD: An Invitation to the Skeptical (2016).

Christian apologetics is a branch of Christian theology that defends Christianity.