Sometimes referred to as the god, sometimes as a man contemporary to Moses, who was son of the god.
During the middle-ages and later, a series of scripts attributed to Hermes Trismegistus, known as the Hermetica were popular.
The texts are usually referred to as the "philosophical" and "technical" hermetica. The former deals mainly with issues of philosophy, and the latter with magic, potions, etc. Among other things there are spells to magically protect objects, thus the term "Hermetically sealed".
In ancient times, the texts were thought to have been written at the dawn of time, but the classical scholar Isaac Casaubon in 1614 showed that the Greek texts betrayed a vocabulary too recent to be so old. Recent research suggests some of these texts may be of pharaonic Egyptian origin, although most of the "philosophical" Hermetica can be dated to around AD 300.
During the Middle ages and the Renaissance, the hermetic scriptures enjoyed great credit and were popular among men of alchemy. The "hermetic tradition" therefore refers to alchemy, magic and the like.