The New Student's Reference Work/Dauphin

Dauphin (da̤′ fĭn), the title given to the eldest son of the king of France, the heir-apparent to the throne.  The title in this form originated with Humbert II, Lord of Viennois, in 1349.  Humbert died childless, and transferred his possessions to Charles of Valois on condition that the heir-apparent to the throne of France bear the title of Dauphin of Viennois.  Dauphin was a title earlier held by some of the feudal lords of France who wore dolphins upon their helmets, or used them as a family crest.