Mercury occupies a peculiarly multivalent position in the depth-psychology corpus, functioning simultaneously as astrological significator, alchemical substance, divine archetype, and psychological function. The literature divides broadly into three streams. First, the Jungian-alchemical tradition treats Mercurius as the supreme paradox: prima materia and ultima materia at once, hermaphrodite, trickster, divine nous, and collective unconscious personified — a figure Jung himself admitted ‘caught hold of’ him personally during the composition of ‘Der Geist Mercurius.’ Abraham’s lexicographic work traces Mercury through the sulphur-mercury theory of metallic generation, the tria prima of Paracelsus, and the hermaphroditic Mercurius duplex of the opus. Second, the Renaissance Neoplatonic tradition recovered by Thomas Moore via Ficino positions Mercury as a mode of ensouled cognition — Apollonian yet embodied, rhetorical rather than speculative, a consciousness that ‘wakens soul’ through eloquence, imagination, and tricksterlike theft from memory. Third, the modern psychological-astrological tradition (Cunningham, Sasportas, Rudhyar, Tarnas) reads Mercury as the natal principle governing communication, intellect, linguistic facility, and the mind-body interface. A productive tension runs throughout: whether Mercury is primarily a mediating function between opposites or an autonomous, destabilizing spirit that resists containment.