Illustration for cover of Dragon 357, created by Andrew Hou - source
Originally found in Dragon #6 (John Sullivan) 1977
Artist unknown - source
"Demogorgon is first mentioned by a scholiast of ca 350-400 AD, who was writing glossary annotations into the margins of Statius's Thebaid. This gloss by an otherwise unknown Christian named Placidus is attributed to Lactantius Placidus in the manuscripts and in the earliest printed editions of Statius' works (Venice, 1483 and 1494); as a result, the writer has been misidentified with Lucius Caelius Firmianus Lactantius and other Christian authors by enthusiastic modern demonologists. The name Demogorgon is introduced in a discussion of book IV line 516 of the Thebaid, which mentions 'the supreme being of the threefold world' (triplicis mundi summum); in a mystical passage that seems to show Jewish influence, as it mentions Moses and Isaiah); the author says of Statius, Dicit deum Demogorgona summum ('He is speaking of the Demogorgon, the supreme god', or perhaps 'He is speaking of a god, the supreme Demogorgon'). Prior to this, there is no mention of the supposed "Demogorgon" anywhere by any writer, pagan or Christian.
In the Early Middle Ages, Demogorgon is mentioned in the tenth-century Adnotationes super Lucanum, a series of short notes to Lucan's Pharsalia that are included in the Commenta Bernensia, the "Berne Scholia on Lucan". By the late Middle Ages, the reality of a primordial "Demogorgon" was so well fixed in the European imagination that "Demogorgon's son Pan" became a bizarre variant reading for "Hermes' son Pan" in one manuscript tradition of Boccaccio's Genealogia Deorum gentilium ("Genealogies of the Gods":1.3-4 and 2.1), misreading a line in Ovid's Metamorphoses.
After Boccaccio Demogorgon is mentioned as a "primal" god in quite a few Renaissance texts, and impressively glossed "Demon-Gorgon," i.e., "Terror-Demon" or "God of the Earth." Seznec, for instance, now spots in Demogorgon an allusion to the Demiurge ("Craftsman" or "Maker") of Plato's Timaeus. For a remarkable early text actually identifying Ovid's Demiurge (1/1, here) as "sovereign Demogorgon," see the paraphrase of Metamorphoses I in Abraham France, The third part of the Countesse of Pembrokes Yuychurch (London, 1592), sig. A2v."
Quote taken from article on the Demogorgon at Wikipedia..