The best-attested teachers are individuals with schools. Valentinus, an Alexandrian who taught at Rome around the middle of the second century, was by one report nearly elected bishop there; his followers, including Ptolemy and Heracleon, remained inside the churches, produced the earliest known commentary on the Gospel of John, and elaborated the most refined version of the pleroma scheme. Basilides, also Alexandrian and slightly earlier, taught a system that the sources describe in two incompatible ways, which is itself a warning about the sources. The Sethians, named for their descent from Seth, are a textual grouping rather than a documented institution, and the Apocryphon of John is their key document.
Marcion is regularly listed alongside these and does not belong there. He distinguished the just god of the Hebrew scriptures from the good and previously unknown god revealed by Jesus, and he assembled the first known fixed Christian canon by editing Luke and ten letters of Paul. But he had no pleroma, no aeons, no divine spark in humanity and no doctrine of saving knowledge. He was a scriptural critic who built a church, and that church survived for centuries.
Movements later called gnostic are best treated case by case. Manichaeism, founded by Mani in third-century Mesopotamia, is a genuinely independent world religion built on a dualist scheme and is not a branch of anything here. Mandaeism survives in Iraq, Iran and diaspora and is the only living religion of this type from antiquity. The medieval Bogomils and Cathars held a dualist theology and rejected the material creation, and older scholarship posited a chain of transmission from late antiquity through the Balkans to Languedoc; that chain is now widely doubted, and some historians argue that the Cathars as described are substantially a construction of the inquisitors who suppressed them.
The modern reception has been vigorous. C. G. Jung read these texts as psychological documents, and the codex named after him was the first of the Nag Hammadi manuscripts to be published. Small ecclesiastical bodies have revived gnostic liturgy since the late nineteenth century. Elaine Pagels's popular treatment in 1979 brought the material to a wide readership, and the texts now circulate far beyond the academy, often flattened into a single doctrine that the sources themselves do not support.