Marcion of Sinope was a theologian in early Christianity. Marcion preached that God had sent Jesus Christ, who was distinct from the "vengeful" God (Demiurge) who had created the world. He considered himself a follower of Paul the Apostle, whom he believed to have been the only true apostle of Jesus Christ; his doctrine is called Marcionism. Marcion published the earliest record of a canon of New Testament books.

Traditionally in Christianity, orthodoxy and heresy have been viewed in relation to the "orthodoxy" as an authentic lineage of tradition. Other forms of Christianity were viewed as deviant streams of thought and therefore "heterodox", or heretical. This view was challenged by the publication of Walter Bauer's Rechtgläubigkeit und Ketzerei im ältesten Christentum in 1934. Bauer endeavored to rethink Early Christianity historically, independent from the views of the current church. He stated that the 2nd-century church was very diverse and included many "heretical" groups that had an equal claim to apostolic tradition. Bauer interpreted the struggle between the orthodox and heterodox to be the "mainstream" Church of Rome struggling to attain dominance. He presented Edessa and Egypt as places where the "orthodoxy" of Rome had little influence during the 2nd century. As he saw it, the theological thought of the "Orient" at the time would later be labeled "heresy". The response by modern scholars has been mixed. Some scholars clearly support Bauer's conclusions and others express concerns about his "attacking [of] orthodox sources with inquisitional zeal and exploiting to a nearly absurd extent the argument from silence." However, modern scholars have critiqued and updated Bauer's model.