The third duke -

Louis-François-Armand de Vignerot du Plessis

3^rd duke of Richelieu, Peer & Marshall of France

1696 - 1788

First Gentleman of the Bedchamber to Louis XV

Patron of both Voltaire and Rameau for the composition of 

'la Princesse de Navarre'

on the occasion of the 

Marriage of the Dauphin of France to the Infanta of Spain

 at Versailles in 23 February 1745

here's a biography

in contrast to Armand Jean du Plessis, cardinal and first duke, this chap actually lived some of the time in the château de Richelieu and embellished it to the sumptious fashion of the day.

The third duke was a famous seducer of ladies of the nobility and was the model for the Vicomte de Valmont in Laclos' 'Les Liaisons Dangereuses' of 1782.

.......first gentleman of the bedchamber.......