Manichaeism was a major religion that was founded by the Iranian prophet Mani in the Sasanian Empire.
Manichaeism taught an elaborate dualistic cosmology describing the struggle between a good, spiritual world of light, and an evil, material world of darkness. Through an ongoing process which takes place in human history, light is gradually removed from the world of matter and returned to the world of light whence it came. Its beliefs were based on local Mesopotamian gnostic and religious movements.
Manichaeism was quickly successful and spread far through the Aramaic-Syriac speaking regions. It thrived between the third and seventh centuries, and at its height was one of the most widespread religions in the world. Manichaean churches and scriptures existed as far east as China and as far west as the Roman Empire. It was briefly the main rival to Christianity in the competition to replace classical paganism. Manichaeism survived longer in the east than in the west, and it appears to have finally faded away after the 14th century in southern China contemporary to the decline in China of the Church of the East during the Ming Dynasty. While most of Manichaeism's original writings have been lost, numerous translations and fragmentary texts have survived.
An adherent of Manichaeism is called, especially in older sources, a Manichee, or more recently Manichaean. By extension, the term "manichean" is widely applied (often used as a derogatory term) as an adjective to a philosophy of moral dualism, according to which a moral course of action involves a clear (or simplistic) choice between good and evil, or as a noun to people who hold such a view.