Here is a belief from Greek Mythology:
KHARON (or Charon) was the ferryman of the dead, an underworld daimon (spirit) in the service of King Haides. He received the shades of the dead from Hermes, who gathered them from the upper world and guided them to the shores of the Akherousian mere. From there Kharon transported them in his skiff to a final resting place in Hades, the land of the dead, on the other side. The fee for his service was a single obolos coin which was placed in the mouth of a corpse at burial. Those who had not received due burial and were unable to pay his fee, would be left to wander the earthly side of the Akheron, haunting the upper world as ghosts.