The Mysterious Stranger is the last novel attempted by the American author Mark Twain. It was worked on periodically from roughly 1890 up until 1910. The body of work is a serious social commentary by Twain addressing his ideas of the Moral Sense and the "damned human race".

Twain actually wrote multiple versions of this story, each unfinished and each involving the character of "Satan". The first substantial version is commonly referred to as The Chronicle of Young Satan and tells of the adventures of Satan, the sinless nephew of the biblical Satan, in an Austrian village in the Middle Ages. The story ends abruptly in the middle of a scene involving Satan entertaining a prince in India, suggesting Twain died before he finished writing it.