Duke of Orléans is one of the most important titles in the French peerage, dating back at least to the 14th century. It was attributed always to princes of the Royal Family and was thus a junior branch of the ruling house. Very often in French History, the Duke of Orléans had an important political role. The Orléans came to the throne with Louis XII (15th century) and Louis-Philippe (19th century). The descendents of the family are the current pretenders to the French throne, and the title has been used by several members of the House.
Henri de Valois, Duc d'Orléans (1551-1589) son of King Henri II; styled Duke of Orléans from 1560, created Duke of Anjou in 1566, succeeded as King Henri III in 1574
Dukes of Orléans of the House of Bourbon
Nicholas Henri de Bourbon, Duc d'Orléans (1607-1611) son of King Henri IV
note that in some sense, all heads of the House of Orleans since 1830 have been entitled to use of the title Duke of Orleans, whether or not they have done so.
Ferdinand Philippe d'Orléans, Duc d'Orléans (1810-1842) eldest son of King Louis Philippe
Guillaume Dubois, formerly tutor to the duke of Orleans, and now his chief minister, caused war to be declared against Spain, with the support of the emperor, and of England and the Netherlands (Quadruple Alliance).
On the majority of the king, which was declared on February 15, 1723, the duke of Orleans resigned the supreme power; but he became first minister to the king, and remained in office till his death on December 23, 1723.