Adolf von Harnack
Adolf Harnack (1851-1930) was a German theologian, scholar and historian.
In some ways von Harnack was a critic of Christian traditions; he argued that all aspects of Christian history should be subjected to academic scrutiny. His work challenged many traditional Christian views, for example he argued that the Gospel of John contained no authentic information about the life of the historical Jesus. However, Harnack's critical approach to Christian history was much less radical than that of the Tübingen school, who challenged the very foundations of Christian faith.
The Tübingen school sought to explain the origin of Christianity in entirely naturalistic terms, and approach that has since become standard. Some see the work of Harnack as a reaction to this development; Harnack embraced the historical-critical method for interpreting the bible, and was very willing to challenge the authenticity of some biblical texts, whilst at the same time he defended key aspects of the traditional interpretation of Christian history, for example by arguing the the book of Acts was composed at an early date.
In 1920 he published a very thorough book on Marcion called Marcion, das Evangelium vom fremden Gott (Marcion and the Gospel of the Alien God), a work which is widely regarded as pivotal to the development of modern study of this subject.
The idea that the Marcionite version of the epistles of Paul pre-dated the conventional version did not fit in well with Harnack's view of history; he was firmly convinced that the epistles of Polycarp and Ignatius were genuine, and thus believed that Catholic copies of the epistles of Paul pre-dated Marcion. For this reason his reconstruction of the Marcionite bible was partly based on the view that Marcion removed from the documents many statements that contradicted Marcionite beliefs.
Online resources by Harnack:
Marcion, an extract from the History of Dogma
The English translation of Marcion and the Gospel of the Alien God is still under copyright, however the German text (which includes Harnack's reconstruction of the Marcionite Bible) has risen into the public domain, and is avalible at Archive.org:
Marcion Das Evangelium Vom Fremden Gott