Hermeticism, also called Hermetism, is a religious, philosophical, and esoteric tradition based primarily upon writings attributed to Hermes Trismegistus ("Thrice Great"). These writings have greatly influenced the Western esoteric tradition and were considered to be of great importance during both the Renaissance and the Reformation. The tradition claims descent from a prisca theologia, a doctrine that affirms the existence of a single, true theology that is present in all religions and that was given by God to man in antiquity.
Many writers, including Lactantius, Cyprian of Carthage, Augustine, Thomas Aquinas, Marsilio Ficino, Giovanni Pico della Mirandola, Giordano Bruno, Campanella, Sir Thomas Browne, and Ralph Waldo Emerson, considered Hermes Trismegistus to be a wise pagan prophet who foresaw the coming of Christianity. An account of how Hermes Trismegistus received the name "Thrice Great" is derived from the The Emerald Tablet of Hermes Trismegistus, wherein it is stated that he knew the three parts of the wisdom of the whole universe. The three parts of the wisdom are alchemy, astrology, and theurgy.
The Poimandres, from which Marsilio Ficino formed his opinion, states that "They called him Trismegistus because he was the greatest philosopher and the greatest priest and the greatest king." The Suda (10th century) states that "He was called Trismegistus on account of his praise of the trinity, saying there is one divine nature in the trinity . . . more