In his Author's Note in this edition of Nostromo, Joseph Conrad provides a detailed explanation of the inspirational origins of his novel.
There he relates how, as a young man of about seventeen, while serving aboard a ship in the Gulf of Mexico, he heard the story of a man who had stolen, single-handedly, a whole lighter-full of silver.
As Conrad goes on to relate, he forgot about the story until some twenty-five years later when he came across a travelogue in a used-boo.