Several philosophers, including Augustine of Hippo, Cicero, Thomas Aquinas, Marsilio Ficino and Giordano Bruno have written about the legend and philosophy of Hermes. Cicero in his De Natura Deorum says that there were five deities named Hermes. The fifth Hermes killed Argus and consequently fled to Egypt where he gave to the Egyptians their laws and letters, and took the Egyptian name Thoth.
The Greek literature under the name of Hermes Trismegistus is concerned mainly with theology, astrology, astral magic, and occult sciences. But there has also developed a philosophical literature under the name of Hermes Trismegistus. The Corpus Hermeticum is one of the most important philosophical Hermetica to come down to us. It is thought to have been composed between the 1st and the 3rd century A.D.
Frances A. Yates in her book Giordano Bruno and the Hermetic Tradition, (Chapter 1, “Hermes Trismegistus”), offers a description of how the Corpus Hermeticum was translated by Marsilio Ficino, working under the instruction of Cosimo de' Medici, in the 15th century. Here’s an excerpt:
About 1460, a Greek manuscript was brought to Florence from Macedonia by a monk, one of those many agents employed by Cosimo de' Medici to collect manuscripts for him. It contained a copy of the Corpus Hermeticum, not quite a complete copy, for it included fourteen only of the fifteen treatises of the collection, the last one being missing. Though the Plato manuscripts were already assembled, awaiting translation, Cosimo ordered Ficino to put these aside and to translate the work of Hermes Trismegistus at once, before embarking on the Greek philosophers. It is Ficino himself who tells us this, in that dedication to Lorenzo de' Medici of the Plotinus commentaries in which he describes the impetus given to Greek studies by the coming of Gemistus Pletho and other Byzantine scholars to the Council of Florence, and how he himself was commissioned by Cosimo to translate the treasures of Greek philosophy now coming into the West from Byzantium. Cosimo, he says, had handed over to him the works of Plato for translation. But in the year 1463 word came to Ficino from Cosimo that he must translate Hermes first, at once, and go on afterwards to Plato; "mihi Mercurium primo Termaximum, mox Platonem mandavit interpretandum". Ficino made the translation in a few months, whilst the old Cosimo, who died in 1464, was still alive. Then he began on Plato.
It is an extraordinary situation. There are the complete works of Plato, waiting, and they must wait whilst Ficino quickly translates Hermes, probably because Cosimo wants to read him before he dies. What a testimony this is to the mysterious reputation of the Thrice Great One! Cosimo and Ficino knew from the Fathers that Hermes Trismegistus was much earlier than Plato.Yates points out that Ficino translated Corpus Hermeticum first because Hermes came earlier than Plato:
Renaissance respect for the old, the primary, the far-away, as nearest to divine truth, demanded that the Corpus Hermeticum should be translated before Plato's Republic or Symposium, and so this was in fact the first translation that Ficino made.
Ficino gave his translation the title of Pimander, which is really the tide of only the first treatise in the Corpus Hermeticum, but which he extended to cover the whole Corpus, or rather the first fourteen of its items which were all that his manuscript contained. He dedicated the translation to Cosimo, and this dedication, or argumentum as he calls it, reveals the state of mind, the attitude of profound awe and wonder, in which he had approached this marvellous revelation of ancient Egyptian wisdom.