Dauphin, the title of the eldest son of a French king. Originally, during the Middle Ages, it was the title of the counts of Vienne, and their county became known as Dauphiné. In 1349 Humbert II, who had no children, sold Dauphiné and the title to Charles of Valois, the eldest son of King John II of France. When Charles became king he transferred the title to his eldest son, and this practice became the rule. After the revolution of 1830 the dauphin title was abolished.