The Greek god Hermes was really a messenger of the gods, as well as a sort of patron saint of anything that had to do with money matters, exchange, sending and receiving goods, and so on.
But he was originally a sort of influxus divinus, a messenger who came down from Olympus to carry out the decisions of the gods, or to communicate the divine word to mortals; and in that form he has been identified with the Egyptian god Thoth, who was the god of writing, of wisdom and intelligence.
Also he has been identified with Mercury, the Roman god, who has much the same character.
A number of those gods were more or less equivalent.
The old Gallic and Celtic gods were identified with the Roman gods, for instance, so we find Celtic forms of Jupiter, Mercury, and others in Gallia Transalpina.
Then Hermes Trismegistus, the thrice-greatest Hermes, is the designation for an entirely legendary figure, a man, not a god.
That may be a historical fact or, more probably, a legendary fact, like Osiris, who is said to have lived as a real human being; and like the second person of the Trinity, Christ; the tradition is that Christ and Osiris were god-men.
This Hermes Trismegistus, according to the legend, was also a god-man, full of divine wisdom, and the father of the so-called Hermetic books.
This is a particular kind of old Greek literature which is said to have originated in the priestly wisdom of Egypt; examples of it are still in existence.
So the relation between that Hermes, called the thrice-greatest Hermes, and the Greek god Hermes is very remote; they are not identical. ~Carl Jung, Visions Seminar, Page 505