From the Super Mario Wiki
Charold is a character found in The Underwhere in Super Paper Mario. He is based on Charon, the ferryman who, for a price, brings deceased souls across the river Styx to Hades in Greek Mythology. His name is a portmanteau on "Charon" and "Harold".
For a fee of four coins, he will ferry the player across the River Twygz. The relation between Charold and Queen Jaydes is not mentioned. It is also unknown whether or not Charold is, in fact, living his "after-game" life or working for Queen Jaydes. The number of 4 coins most likely is a reference to the number 4 being an unlucky number in Japanese lore, sounding quite similar to the word for death in Japanese.