Gnosticism (Greek: γνῶσις gnōsis, knowledge) refers to diverse, syncretistic religious movements in antiquity consisting of various belief systems generally united in the teaching that humans are divine souls trapped in a material world created by an imperfect god, the demiurge; this being is frequently identified with the Abrahamic God, and is contrasted with a superior entity, referred to by several terms including Pleroma and Godhead. Depictions of the demiurge - the term originates with Plato's Timaeus - vary from being as an embodiment of evil, to being merely imperfect and as benevolent as its inadequacy permits. Thus, broadly speaking, Gnosticism was a dualistic religion, influenced by and influencing Hellenic philosophy, Judaism (see Notzrim), and Christianity; however, by contrast, later strands of the movement, such as the Valentinians, held a monistic world-view. This, along with the varying treatments of the demiurge, may be seen as indicative of the variety of positions held within the category.
The gnōsis referred to in the term is a form of revealed, esoteric knowledge through which the spiritual elements of humanity are reminded of their true origins within the superior Godhead, being thus permitted to escape materiality. Consequently, within the sects of gnosticism only the pneumatics or psychics obtain gnōsis; the hylic or Somatics, though human, being incapable of perceiving the higher reality, are unlikely to attain the gnōsis deemed by gnostic movements as necessary for salvation. Jesus of Nazareth is identified by some Gnostic sects as an embodiment of the supreme being who became incarnate to bring gnōsis to the earth. In others (e.g. the Notzrim and Mandaeans) he is considered a mšiha kdaba or "false messiah" who perverted the teachings entrusted to him by John the Baptist. Still other traditions identify Mani and Seth, third son of Adam and Eve, as salvific figures.
Whereas formerly Gnosticism was considered by some a heretical branch of Christianity, it now seems clear that traces of Gnostic systems can be discerned some centuries before the Christian Era. Gnostic sects may have existed earlier than the First Century BCE, thus predating the birth of Jesus. The movement spread in areas controlled by the Roman Empire and Arian Goths (see Huneric), and the Persian Empire; it continued to develop in the Mediterranean and Middle East before and during the Second Century and Third Centuries. Conversion to Islam and the Albigensian Crusade (1209–1229) greatly reduced the remaining number of Gnostics throughout the Middle Ages, though a few isolated communities continue to exist to the present. Gnostic ideas became influential in the philosophies of various esoteric mystical movements of the late 19th and 20th Centuries in Europe and North America, including some that explicitly identify themselves as revivals or even continuations of earlier gnostic groups.