I. HERMES MERCURIUS TRISMEGISTOS
When looking at the rules and supplements to Ars Magica, one becomes aware of two great truths. The first is that the authors have put together an incredibly good role playing game that captures perfectly the feel of medieval magic, especially as seen through our 20th-century lenses. The second is that the authors have no idea who "Hermes" is, in the context of medieval magic. They seem to think that what is referred to as the "Hermetic tradition" descends from the worship of the Greek god Hermes through the cult of his Roman eidolon Mercury to the post-Roman survivals of knowledge in the Middle Ages.
This is incorrect. The "Hermetic tradition" of Western magic, which is one of the most powerful forces in the "underground stream" of Western culture, has less to do with the Roman god Mercury than it does with hermetic sealing.
https://ia801809.us.archive.org/18/items/hermes-trismeistos/Hermes%20Trismeistos.pdf