The alleged teacher the magical system known as Hermetism of which high magic and alchemy are thought to be twin branches. The name Trismegistus means thrice greatest Hermes, and is the title given by the Greeks to the Egyptian god Thoth or Tehuti, a lord of wisdom and learning.
At one time the Greeks thought two gods inseparable. Thoth governed over mystical wisdom, magic, writing and other disciplines and was associated with healing, while Hermes was the personification of universal wisdom and the patron of magic.
The myths go further. Both gods are associated with sacred writings. As scribe for the gods, Thoth was credited with all the sacred books. In various Egyptian writings he is called "twice very great" and "five times very great." Hermes is credited with writing 20,000 books by Iamblichus (ca. 250-300 BC), a Neo-platonic Syrian philosopher, and over 36,000 books by Manetho (ca. 300 BC), an Egyptian priest who wrote the history of Egypt in Greek, perhaps for Ptolemy I.
The combined myths of these gods report that both Thoth and Hermes revealed to humankind the healing arts, magic, writing, astrology, science, and philosophy. Thoth wrote the record of the weighing of the souls in the Judgment Hall of Osiris. Hermes led the souls of the dead to Hades.
The English occultist Francis Barrett in Biographia Antiqua wrote that Hermes "communicated the sum of the Abyss, and divine knowledge to all posterity"
According to legend Hermes Trismegistus is said to have provided the wisdom of light in the ancient mysteries of Egypt. "He carried an emerald, upon which was recorded all of philosophy, and the caduceus, the symbol of mystical illumination. Hermes Trismegistus vanquished Typhon, the dragon of ignorance, and mental, moral and physical perversion."
Surviving Hermes Trismegistus is the wisdom of the Hermetica, 42 books that have profoundly influenced the development of Western occultism and magic.