Cyrus is a brilliant, mid-forties engineer from Massachusetts who previously oversaw railway construction across the United States. He possesses a strong work ethic and acts as the natural leader of the castaways. His extensive practical knowledge of chemistry, metallurgy, and physics drives the group's survival efforts on the island. He consistently places the safety of the group ahead of his own comfort.

Gideon is an energetic and fearless journalist who chronicles the group's experiences in his notebook. He acts as the secondary voice of reason and uses his diverse, world-traveled background to assist in problem-solving. He serves as a highly capable hunter and gathers essential information for the group's survival. His physical resilience matches his quick intellect during dangerous encounters.

Nebuchadnezzar is an agile and cheerful thirty-year-old man who was formerly enslaved but freed by Cyrus. He manages the group's domestic tasks and creatively cooks their meals using local wildlife. His deep loyalty to Cyrus drives him to search relentlessly when the engineer initially goes missing. He maintains a steadfastly positive attitude during severe weather and food shortages.

Bonadventure Pencroff is a tanned, late-thirties sailor with an enterprising and restless spirit. He frequently pushes the group to undertake ambitious projects, such as building watercraft for exploration. His practical maritime skills prove highly valuable for navigating the island's coastal waters. He views the deserted island not as a prison but as a territory waiting for civilization.

Harbert is a fifteen-year-old orphan who possesses an encyclopedic knowledge of botany and zoology. He identifies various plant and animal species on the island, contributing directly to the group's food supply and physical comfort. He actively seeks to learn from the older men and assist in their daily labors. He acts bravely during unexpected encounters with the island's predators.

Bob Harvey is a ruthless pirate captain leading a crew of escaped convicts from Norfolk. He commands a heavily armed vessel and seeks to establish a new base of operations by force, treating any existing inhabitants as enemies.

Ayrton is a solitary Englishman who has lived in complete isolation for over a decade following his involvement in maritime crimes. His time alone has severely affected his social skills and physical appearance. He struggles with feelings of unworthiness as he slowly attempts to reintegrate into human society alongside the other castaways.

Top is Cyrus Smith's loyal canine companion. He assists the men by hunting small game and alerting them to unseen dangers in the dense jungle. His sharp senses frequently guide the castaways toward crucial discoveries.

Jupiter is a native orangutan captured by the men after they find him inside their home. He quickly learns to perform basic tasks and becomes an intelligent, helpful presence around their camp.