William Legrand: He is a well-educated man but had fallen on hard times and is poor when the story begins. He chooses to live isolated from the world in a small hut he built on Sullivan's Island, not too far from Charleston, South Carolina. He has sudden mood swings, alternating between enthusiasm and depression. His servant and the narrator thinks he may be insane because he was bitten by a gold bug. He's very intelligent as he's able to figure out the cryptogram of Captain Kidd. We learn he has a playful side when he tells the narrator he really didn't need to use the gold bug. He used it to punish the narrator for thinking he had gone mad.
Narrator: A physician who tends to be a reliable narrator, meaning the reader can trust that he's telling the story as it really happened. He's concerned about Legrand's mood swings and thinks his servant may be right about Legrand going insane. He shows himself to be a caring physician and/or friend when he receives Legrand's message from Legrand's servant to come to Sullivan's Island.
Jupiter: The freed black servant of Legrand who lives with him on Sullivan's Island. He runs errands for him so Legrand won't have to have more contact with the outside world than he wants to. He seems to genuinely care about Legrand as he helps him when Legrand is bitten by the gold bug. Jupiter isn't educated, as is seen when he mixes up which is the left eye of the skull. Legrand does "order" Jupiter to climb the tree, however, suggesting that even though he's free, Jupiter and Legrand still think of Jupiter in slave-like terms.
Newfoundland dog: Lives with Jupiter and Legrand at Sullivan's Island. The dog is responsible for Legrand finding the picture of the skull on the back of the parchment paper on which Legrand had sketched the gold bug.
Gold bug: Considered a character since it is the bite of this beetle who begins the treasure hunt for Captain Kidd's treasure chest. In ancient Egypt, the beetle, or scarab, was considered lucky by the Egyptians. In this case, it proves to be a very good sign of luck for Legrand.