In the Platonic, Neopythagorean, Middle Platonic, and Neoplatonic schools of philosophy, the demiurge (/ˈdɛmi.ɜːrdʒ/) is an artisan-like figure responsible for fashioning and maintaining the physical universe. The Gnostics adopted the term demiurge. Although a fashioner, the demiurge is not necessarily the same as the creator figure in the monotheistic sense, because the demiurge itself and the material from which the demiurge fashions the universe are both considered consequences of something else. Depending on the system, they may be considered either uncreated and eternal or the product of some other entity.

The word demiurge is an English word derived from demiurgus, a Latinised form of the Greek δημιουργός or dēmiurg\xf3s. It was originally a common noun meaning "craftsman" or "artisan", but gradually came to mean "producer", and eventually "creator". The philosophical usage and the proper noun derive from Plato's Timaeus, written c. 360 BC, where the demiurge is presented as the creator of the universe. The demiurge is also described as a creator in the Platonic (c. 310–90 BC) and Middle Platonic (c. 90 BC–AD 300) philosophical traditions. In the various branches of the Neoplatonic school (third century onwards), the demiurge is the fashioner of the real, perceptible world after the model of the Ideas, but (in most Neoplatonic systems) is still not itself "the One". In the arch-dualist ideology of the various Gnostic systems, the material universe is evil, while the non-material world is good. According to some strains of Gnosticism, the demiurge is malevolent, as it is linked to the material world. In others, including the teaching of Valentinus, the demiurge is simply ignorant or misguided.