Ophis (greek ophis: serpent)
Cornelius Agrippa wrote: "Pherecydes the Syrian describeth the fall of the devils, and that Ophis, that is the devilish serpent, was the head of that rebelling army" (Three Books of Occult Philosophy, Book III, Ch. 18).
This history of Ophis as a demon is particularly unusual: he appears to be one of those creatures carried over from earlier greek mythology, eventually making the transition from Titan (and godhead) to being mis-identified as a possible Lucifer.
Ophion is the presumed origin of this name, a titan who had the form of an enormous serpent. Ophion, by some earlier greek myths, ruled Olympus with his wife, Eurynome, long before the appearance of Zeus and the other olympian gods. He was displaced by Cronus, another titan, who was later deposed by the thunder god.
A sect of Gnostics named the Ophites worshipped Ophis as the serpent (whom was later reincarnated as Christ) in Genesis¹. Ophis is identified as the serpent who persuaded Adam and Eve to eat the fruit from the tree of knowledge, thus disobeying the Demiurge's attempt at witholding knowledge from them.
¹:The Ophites may still exist(?) -- an organization called The Ophis Foundation, based around Thelemic Gnosticism, seems to be alive and well somewhere in the world. Any information on this is welcome.