Charon is the ferryman of the Underworld. In various depictions, Charon is just an old man who ferries the living through the River Styx. In other depictions, he is shown as an undead, with grotesque traits, and is sometimes depicted as been attached to the boat by his torso, essentially ending in him been the boat himself.
For a fee, he would bring the dead across the River Styx that separated the world of the living from the world of the dead. Those who could not pay the fee were forced to wander the shores of the river as Wraiths for eternity (or one hundred years depending on the recount).