Adolf von Harnack was a German Lutheran theologian and prominent church historian. He produced many religious publications from 1873 to 1912. Harnack traced the influence of Hellenistic philosophy on early Christian writing and called on Christians to question the authenticity of doctrines that arose in the early Christian church.
His father, Theodosius, was professor of practical theology in the University of Dorpat and the author of a number of well-known theological studies. His maternal grandfather, Gustav Ewers, edited and published Muenter's Handbook of the History of Dogma.
The young Harnack studied at Dorpat between 1869 and 1872 and at Leipzig, where he became Privatdocent in 1874 and associate professor in 1876.
In 1879 he was called to the professorship of Church history in the University of Giessen; from there he went to Marburg in 1886, and after 1890 he served on the faculty of the University of Berlin until 1928. Harnack was also director of the Royal Library, later called the Prussian State Library, from 1905 to 1921.
He argued that Christianity must free itself from theological dogmatism and seek, through rigorous study of the history of Christian doctrine, to return to the religion of the earliest church, i.e., the gospel of Jesus himself. Thus, he also rejected the Gospel of John as unhistorical and criticized the Apostles' Creed as adding doctrinal points never intended by Jesus or the earliest leaders of the Christian church.
Patrum apostolicum opera, Texte und Untersuchungen zur Geschichte der altchristlichen Literatur, Geschichte der altchristlichen Literatur bis Eusebius, Dogmengeschichte, Das Wesen des Christentums (1900) (What is Christianity?), Die Mission und Ausbreitung des Christentums in den ersten drei Jahrhunderte, The Mission and Expansion of Christianity in the First Three Centuries.