If the game made me fight Cerberus I might have just quit the game. The massive three-headed dog often referred to the hound of Hades guards the gates of the Underworld to prevent the dead from leaving. Once Zagreus reaches the Temple of Styx, Cerberus guards its exit. Zagreus must find a Satyr Sack, Cerberus’s favourite snack, as a bribe to leave the area.
Charon is the boatman of the river Styx, responsible for ferrying deceased souls across the river and into the underworld. In Greek mythology, he required a single obol – placed into the mouth before burial – as payment for his services. If it was not paid the soul in question would be left to wander the banks of the Styx for a hundred years.
Charon’s services in-game are, unfortunately, much more expensive; he functions as the game’s shopkeeper, selling Zagreus various power-ups, items, and boons in return for obols. While all the gods (except Chaos) can use Charon’s shop to offer their boons to Zagreus, Hermes is the only god with whom Charon has a lasting professional relationship.
Thanatos is the personification of death. He is one of Nyx’s many children and the twin brother of Hypnos. As the embodiment of death, Thanatos has many duties requiring him to venture up into the mortal realm. He apparently dislikes the mortal realm, in particular, how bright it can get.
Thanatos occasionally appears at the beginning of regular encounters and challenges Zagreus to see which of them can slay more shades. If Zagreus either kills more enemies than Thanatos does or ties his total, he will award Zagreus a Centaur Heart in addition to the regular room-clear reward.
Hypnos is the embodiment of sleep. He is one of Nyx’s many children and the twin brother of Thanatos. Hypnos watches over the procession of newly-arrived shades coming before Hades, checking their names off his list. You’ll find him often sleeping on the job.
Hypnos greets Zagreus whenever the prince is killed and returns him to the House via the Pool of Styx. Often giving unhelpful advice and a quip about whichever enemy or natural force did Zagreus in.
Another non-god makes the list but what’s hell without a tortured soul? Sisyphus is a former king sentenced to an eternity of punishment in Hell for attempting to cheat death. He succeeded twice, each time only temporarily before the consequences caught up with him. His punishment is to roll a boulder up a steep hill. The boulder, however, always rolls back down the hill before he reaches the top.
In spite of his never-ending punishment, Sisyphus is generally good-humoured and polite, having had ample time to reflect on his deeds in life. He refers to his boulder as “Bouldy”, treating “him” as a friend and confidante.