Many traditions are named after a founder real or imaginary and Hermeticum is no exception. The texts that make up the Hermetic tradition are said to be written by an enlightened teacher called Hermes Trismegistus, but who was this mysterious author.
The texts themselves never explain and there are multiple theories put forwards as part of the tradition since those days.
The most common and convincing theory is that Hermes Trismegistus or the “Egyptian Hermes” as he was often called is a composite god consisting of a combination of The Greek Hermes who was a figure of cunning, guile and both a herald and messenger but also (unlike Trismegistus) was a thief and trickster. This figure it is thought combined with the Egyptian god of magic, mystery and writing Thoth, who was the scribe of the gods and possessed the secrets of the universe.
There are however theories that he was the younger Hermes who was the actual grandson of the god Hermes. Or a reincarnated spiritual teacher, who thought repeated lives teaches mankind throughout history, helping a guiding the human race.
In the early writings, Hermes was always taken to be a literal figure. In later times however people have often interpreted him as a symbolic figure who represents the ideal enlightened state. Some people even believe him to be an actual spirit that works through different authors like a divine muse teaching through their words and writings.