This strong devotion continued throughout the Ptolemaic and Roman periods, i.e. when Egypt had entered its Late Period and was Hellenized. Both Jewish settlers as well as Greeks tried to establish some link with Thoth (the second-century BC romancer Artapanus assimilated Moses to Thoth !).

The Greeks, who started to settle in Egypt under Pharaoh Amasis (570 - 526 BC), associated Thoth with Hermes. The latter was also linked with the Moon, medicine, the realm of the dead, inventiveness, trickery and functioned as messenger of the gods. Hence, in the Hellenistic period, Thoth became the "word" or "logos", interpreting the divine will to humanity. The Lycaonians saw in him the apostle Paul and the Stoics regarded him both as "logos" and demiurge.

 

Thoth, god of writing, magic, healing & wisdom
after Champollion, J.F. : Panthéon Egyptien, planche 30C

Finally, the epithet "Trismegistus" (thrice greatest) acquired canonicity in the Roman period. For although, in the beginning, there was no doubt that the Greek god Hermes was equivalent to the Egyptian god Thoth, we read Cicero enumerate no less than five different historical individuals who had claimed the name "Hermes". Hence, the name "Hermes Trismegistus" invoked a relatively human Hermes distinct from the messenger of the deities, an association made foremost by people of Greek culture.

In the Greek magical papyri, we clearly discern an Egyptian Hermes Trismegistus, a cosmic deity with whom the magician (in Egyptian style - cf. the ritual assumption of god-forms) could identify. In the "Hermetica" (the Corpus Hermeticum, a total of seventeen treatises, written from the late first to the late third centuries AD), Trismegistus is usually invisaged as a sage who lived in a remote period, conversing with the deities, though they also speak of him as a divine being ... Apparently, Hermes Trismegistus was conceived as hovering between the divine and human world, which, being a mediator, was an advantage.

Arab tales invoke three persons called "Hermes". The first of them, Hermes Trismegistus, lived before the Flood and was the grandson of Adam. He wrote books, had knowledge about celestial and terrestial things, built the pyramids and was the patron of science and mathematics. The second Hermes was an inhabitant of Babylon who lived after the Flood. A scientist, medical doctor, philosopher and mathematician, he was the teacher of Pythagoras. Hermes the third lived in Egypt as a physician and a philosopher (Balinas ?). 

These myths were accepted by Muslim alchemists, and so they called their art the "Hermetic Art". The influence of the Egypto-Alexandrian hermetical doctrine on early Muslim astro-magical, philosophical and alchemical thought can be well explained, if we realize that when the "pagan" institutions and places of worship & learning (cf. the Platonic Academy, the temples & libraries of Alexandria & Philae) were closed by Christian authorities (Theodosius, Justinianus), the teachings & cult of the Moon-god Thoth-Hermes fled to Harran. In the 7th century AD, this late Egypto-Alexandrian hermetism submitted to the invading Muslim forces, to whom they showed their "holy" scriptures. In them, the unity of God was truly asserted.

"Syrian pagans from Harran were also widely employed in translation ; they were star-worshippers and diligent astrologers. These Sabians, as the Arabs called them, possessed exceptional skills as linguists, and the ease with which they acquired Arabic recommended them to the courts at Baghdad ..."
Holmyard, E.J. : Alchemy, Dover - New York, 1990, p.68.