Cyrus Smith (named Cyrus Harding in some English translations) is one of the protagonists of Jules Verne's novel The Mysterious Island published in 1875. He is an officer in the Union Army during the American Civil War 1).
He is selfless, noble, honest, courageous, and utterly devoted to his companions. His practical knowledge of physics, chemistry, botany, navigation, and many other fields enables the Mysterious Island's colonists to quickly establish a thriving mini-civilization in isolation from the rest of the world. Smith is, however, annoyed and secretive regarding the fact that the colony has been mysteriously saved many times by a benefactor who refuses to reveal himself, causing his own achievements to seem less significant 2).
In Le retour du capitaine Nemo, Nemo wonders what happened to Cyrus Smith.