Professor Sherman is a 66-year-old former arithmetic teacher from San Francisco who desires a year of solitary balloon travel. He is highly intelligent and scientifically minded. His honest and practical nature grounds his extraordinary experiences. He finds great joy in exploring new lands and marveling at unique inventions.

Mr. F. is an elegantly dressed gentleman who serves as the representative of French culture on the island of Krakatoa. He lives in a magnificent French-style mansion and offers French cuisine to the residents when it is his turn to cook. He functions as a knowledgeable and hospitable guide to the island's hidden society.

The enthusiastic political leader of Professor Sherman's hometown. He goes to great lengths to orchestrate a massive balloon-themed parade for the returning explorer. His actions are largely driven by a desire to share in the returning hero's fame.

The ambitious founder of Tomes Aeronautical Studios in San Francisco. Eager to participate in the city's grand celebrations, he designs an elaborate horse-drawn couch lifted by balloons.

The son of Mr. F. and a youth living in the Krakatoan community. Like the other children on the island, he enjoys creating and riding elaborate amusement rides that utilize the local technology.

The original founder of the Krakatoa colony and a survivor of a shipwreck. After discovering the island's immense wealth, he recruited twenty families from San Francisco to build a secret cooperative society. He acts as a sensible and organized leader for the community.

The wife of the colony's founder. She lives in a spectacular Moroccan-style home filled with unusual labor-saving inventions. She gladly pitches in when the community needs specialized equipment crafted.

One of the children of the island's founder. M-1 helps manage the daily operations of the specific restaurant household and operates the home's mechanical features.

The second child of Mr. and Mrs. M. M-2 participates in the family's restaurant duties and enjoys playing in the mechanized rooms of their house.

The resident of Krakatoa who represents British culture. He hosts the island's citizens for communal meals in his large cottage.

The wife of Mr. B. She assists in running the British-style cottage and preparing traditional meals for the island's rotating dining schedule.

The resident of Krakatoa who represents Chinese culture. He lives in a pagoda-style house and serves traditional meals to the community during his designated days.

The commanding officer of the ship that rescues a stranded balloonist in the Atlantic Ocean. He notes strange details about the balloon wreckage and helps arrange for his passenger's safe return to land.

The top medical official in San Francisco. He is tasked with ensuring the health and comfort of the city's returning hero during the grand parade and subsequent lecture.