Demogorgon is a deity or demon, associated with the underworld and envisaged as a powerful primordial being, whose very name had been taboo. Although often ascribed to Greek mythology, the name probably arises from an unknown copyist's misreading of a commentary by a fourth-century scholar, Lactantius Placidus. The concept itself though can be traced back to the original misread term demiurge.
The origins of the name Demogorgon are not entirely clear, though the most prevalent scholarly view now considers it to be a misreading of the Greek δημιουργόν (dēmiourgon, accusative case form of δημιουργός, 'demiurge') based on the manuscript variations in the earliest known explicit reference in Lactantius Placidus (Jahnke 1898, Sweeney 1997, Solomon 2012). The variants cited by Jahnke include the Latin "demoirgon", "emoirgon", "demogorgona", "demogorgon", with the first critical editor Friedrich Lindenbrog (Fridericus Tiliobroga) having conjectured "δημιουργόν" as the prototype in 1600. Various other theories suggest that the name is derived from a combination of the Greek words δαίμων daimon ('spirit' given the Christian connotations of 'demon' in the early Middle Ages)—or, less likely δῆμος demos ('people')— and γοργός gorgos ('quick') or Γοργών Gorgon, the Ancient Greek triad of monster-goddesses whose origins extend to the fifteenth century BC, or much earlier (as suggested by Marija Gimbutas).
Demogorgon is first mentioned in the commentary on Statius's Thebaid often attributed in manuscripts to a Lactantius Placidus, (c. 350-400 AD). The Lactantius Placidus commentary became the most common medieval commentary on the poem by Statius and is transmitted in most early editions up to 1600. The commentary has been attributed incorrectly to a different Lactantius, the Christian author Lucius Caelius Firmianus Lactantius, even though the commentator appears to have been Mithraic.