Who guided souls to the underworld in Greek mythology?

Charon is the figure in Greek mythology who is specifically responsible for guiding souls across the rivers that separate the world of the living from the underworld, particularly the river Styx. He is often depicted as a sturdy, grim figure who ferries the dead to their final resting place, charging a fee for passage, which is why it was customary for the living to place an obol (a small coin) in the mouth of the deceased to pay for this journey. Charon's role is crucial, as without him, souls would be left wandering the shores of the rivers, unable to enter the underworld.

While Hermes does have a role as a psychopomp — a guide of souls to the afterlife and often associated with traveling between the worlds — Charon is the designated ferryman specifically linked to the passage across the Styx. Thanatos, meanwhile, is the personification of death itself, representing the aspect of dying, rather than guiding souls. Hades is the god of the underworld, ruling over the realm of the dead but not specifically guiding souls. Therefore, Charon is the most accurate answer in the context of who guides the souls to the underworld.