Edward "Ned" Malone is a reporter for the Daily Gazette who seeks dangerous exploits to impress the woman he loves. Recognizing his own imaginative nature, he sometimes doubts his courage but possesses an overpowering fear of seeming afraid. This insecurity drives him to volunteer for an unproven and highly dangerous expedition to South America in hopes of returning a famous hero.

Professor Challenger is a massive, confident, and booming scientist who claims to have discovered prehistoric life in South America. He embraces his abrasive reputation, viewing himself as a man of destiny who brings monumental discoveries to the world. He acts with absolute certainty and readily uses physical force against journalists who doubt his word.

Lord John Roxton is a famous hunter, explorer, and veteran of South American expeditions. He views risk and danger as necessary ingredients for an exciting life, preferring perilous sporting opportunities over safe existence. He carries a formidable reputation from his past efforts fighting slavers.

Professor Summerlee is a single-minded, closeminded academic with a deep love for chalk fossils. He strictly adheres to empirical standards of proof and refuses to believe anything he cannot see with his own eyes. He joins the expedition primarily to expose Challenger as a scientific fraud.

Gladys Hungerton is a young woman who idealizes famous men of action, specifically adventurous historical figures. She desires a husband who defies death and commands public awe, finding Ned too safe and inexperienced for her tastes.

McArdle is the Scottish editor at the Daily Gazette who oversees Ned's journalistic work. He encourages Ned to expose Challenger as a fraud and facilitates the expedition by arranging for Ned's letters to serve as newspaper dispatches.

Tarp Henry is a writer and bacteriologist who works with Ned. He provides Ned with background information on Challenger's hostile reception in the scientific community, firmly believing that Challenger's prehistoric animal drawings are forgeries.

Mrs. Challenger is the wife of the volatile Professor Challenger. She attempts to manage her husband's aggressive tendencies, sometimes resulting in him placing her on a tall "stool of penance" as a bizarre form of domestic discipline.

Zambo is a dark-skinned, immensely strong local man hired to assist the explorers. He serves as a willing and physically powerful helper during their journey toward the mysterious plateau.

Gomez is a local guide employed to help the explorers travel through the treacherous Amazonian woods. He possesses knowledge of the local terrain and the superstitions surrounding the region.

Manuel is one of the hired guides assisting Challenger's group. He works alongside Gomez to help the Europeans carry supplies and clear paths through the dense South American vegetation.

Pedro Lopez is a Spanish slave driver who operated in South America before the events of the novel. He was defeated by Lord John Roxton, who armed a group of slaves to win their freedom.

Maple White is a deceased artist and poet who originally discovered the plateau. His surviving sketchbook, which contains drawings of impossibly large creatures, provides Challenger with the foundational evidence for the expedition.

James Colver is an American who traveled with Maple White to the South American plateau. His grim remains serve as a warning to the expedition team about the physical dangers of scaling the cliffs.

Jack Ballinger is a famous jockey who becomes belligerent and violent when drinking. He barricades himself in a room with a pistol before being subdued by Lord John Roxton.

Ray Lankester is a scientist and friend of Professor Challenger. He authored a monograph theorizing the physical appearance of the stegosaurus, which Challenger uses to corroborate Maple White's sketchbook drawings.

Mr. Hungerton is Gladys's pretentious father. He hosts a tedious dinner that Ned must suffer through before speaking privately with Gladys.