Ernst Robinson, occasionally documented as Ernest, serves as the second eldest son in the Robinson family, positioned between elder brother Fritz and younger siblings Jack and Francis. He is approximately thirteen during the family’s shipwreck.

Endowed with an intellectual and observant nature, Ernst engages in scientific inquiry and practical problem-solving, identifying species and geographical features. Initially perceived as inclined toward indolence by his father, he evolves through survival tasks, applying his studiousness to catalog resources, test edible plants using the family’s pet monkey, and devise preservation techniques like salting fish and preparing caviar.

Throughout the island adaptation, Ernst contributes logical reasoning and theoretical knowledge—proposing raft construction for safer shore access and hypothesizing about the island’s geological origins as a potential continental land bridge. He meticulously journals their experiences.

Interpersonally, he exhibits rivalry with Fritz over leadership decisions and later, competition for the affections of shipwreck survivor Roberta. Conflicts emerge during expeditions, such as navigation disputes when Ernst loses his compass and challenges Fritz’s judgment. These tensions resolve via parental guidance and shared adversities, including pirate confrontations demanding cooperation.

Ernst matures from reserved introspection to active involvement in family defense, engineering booby traps against pirates. Post-rescue conclusions vary: some adaptations depict him departing for European education, while others show him remaining on the island with part of the family.

Across all narratives, Ernst’s specialized role highlights cerebral strengths, complementing Fritz’s physical prowess and his younger brothers’ exuberance. His journey underscores resilience forged through applied knowledge and collaborative effort.