The person most often associated with the title of dauphin is Louis XVII, second son of Louis XVI and Marie Antoinette, uncrowned king of France 1793-1795. Following the French Revolution and execution of his father, the crown automatically passed to the young Louis XVII who was imprisoned along with the rest of the royal family. Louis XVII being too young to have any issue, the boy was also the last to hold the title.
The child-king was said to have died a premature death in 1795, at the age of 12, partly due to mistreatment by his jailer, Antoine Simon. However, rumours persisted that the child that had died in prison was not the actual Dauphin and that Louis XVII had escaped and was in hiding, having been switched with an other child in prison. For the next 205 years and until 2000, when DNA analysis revealed beyond reasonable doubt that the remains of the imprisoned youngster were really those of Louis XVII, royalists in France harboured the hope that the royal line had been preserved and numerous impostors gained fame and/or profit claiming to be the Dauphin.
From its earlier meaning of heir apparent, the Dauphin figure evolved into the archetypical pretender and the word is now used more often in the context of the latter and more often than not applies to political heirs such as those that wait in the wings behind a towering figure. On the opposite side of the seriousness with which the term is used in politics we find Mark Twain's superbly comical con man and pretend dauphin in Huckleberry Finn.