Charon, the ferryman who carried dead souls across a river into hell, is usually depicted as an old man with burning eyes. His old age, however, is a “green old age”, as Virgil describes in Book VI of the Aeneid. Charon, as the son of Nyx (Night) and Erebus (Darkness), is immortal.
In Graeco-Roman mythology, it is important to remember that being immortal does not mean possessing immortal youth. (Recall the example of Aurora’s beloved Tithonus.) In Charon’s case, his immortality is an immortal, unchanging old age.
As the son of Nyx and Erebus, both of them primeval deities (or rather, personifications of natural phenomena), we can date Charon back to the pre-Olympian age. Of course, different authors give different accounts of Charon’s family. Hesiod names Chaos as Charon’s father; in another account, however, he is the son of Chronos (time).
But in a sense, it is stylistically appropriate to consider Charon the offspring of Nyx and Erebus, because as their son he becomes brother to Geras, Thanatos, Nemesis, and Eris. Geras is the god of Old Age; Thanatos the god of Death; Nemesis is the goddess of vengeance; Eris the goddess of strife — quite a striking brood, and it would also explain, thematically, why Charon is the ferryman of hell.
The actual word for Charon’s role is “psychopomp”: a guide of souls, a being responsible for leading the dead to their final destination. In Graeco-Roman mythology Charon shares this title with the god Hermes (Mercury), whose task is to guide the shades from the world above into the world below; once in hell, it is Charon’s task to ferry them across the river.
The river has alternately been named as Acheron or Styx. The confusion may have stemmed from Virgil, who associates Charon with both rivers. Sometimes Virgil even describes the water as a lake (e.g., Aeneid Book VI, line 393). The ancients called the lake Acherusia.
For a dead soul to be ferried across the river/lake, certain conditions must be met. The soul must pay Charon a fee, usually a coin. This is reflected in the ancient burial practice of placing a cheap coin under a dead person’s tongue (or on their lips, or each of their eyes) for use in the afterlife. So if a person has not been given proper funeral rites, they would most likely lack a coin, which means that unless they receive burial, they have to wander the shores of the river for one hundred years before they are allowed to cross. Hence the importance of proper burial.
Charon’s task, then, is to row dead souls across the river for eternity. Every once in a while (at least in ancient days) things are made interesting for him by the arrival of a living person. The journey to the underworld and back to the realm of the living, known as “katabasis”, is a requisite step in the development of an ancient Greek or Roman hero:
Orpheus goes to hell to bring back his dead wife Eurydice
Odysseus goes to hell to seek the prophecies of Tiresias
Theseus and Pirithous go to hell to carry off Persephone (they failed)
Hercules goes to hell to complete the last and most difficult of his labors: to put the hound Cerberus in chains
Aeneas goes to hell to meet his father and survey his descendants, among them Julius Caesar and Augustus. (Hell is not just a place for the dead; unborn souls live on the other side of Lethe, the river of forgetfulness.)
One of the many obstacles that a hero undergoing katabasis faces is Charon’s refusal to ferry them across the river. It is against divine law, as Charon says, for his boat to carry living souls. However, he did give in several times: Orpheus charmed him with his lyre, Hercules intimidated him with his strength, and Aeneas carried the golden bough. But to go against divine law always incurs punishment. After helping Hercules, Jupiter put Charon in chains for one year. Some ancient authors have built on this story and decided that after helping each hero, Charon spent a year in chains. This explains his displeasure at seeing Aeneas approaching the river—that is, until he perceives the golden bough. The person who plucks the golden bough has received divine sanction to enter hell as a living man.