Saint John the Theologian, also known as Saint John the Apostle, is one of the twelve apostles of Jesus Christ and is traditionally credited with writing the Gospel of John, three epistles, and the Book of Revelation. He is often referred to as the "Beloved Disciple" and is recognized for his deep theological insights and emphasis on love. John is believed to have lived into old age, spending much of his later life in Ephesus. His writings have had a significant impact on Christian theology, particularly regarding the nature of Christ and the concept of eternal life. He is venerated as a saint in many Christian traditions, including Catholicism, Orthodoxy, and Protestantism.