César de Bourbon, duc de Vendôme

César of Bourbon-Vendôme (César I, Duke of Vendôme, Beaufort and Etampes) (Château de Coucy, 3 June 1594 – Paris, 22 October 1665) was the son of Henry IV of France and his mistress Gabrielle d'Estrées.

He was legitimized in 1595, and was created the first Duke of Vendôme by his father in 1598. The next year, he became Duke of Beaufort and Duke of Étampes upon the death of his mother.

On 16 July 1608, at the Château de Fontainebleau, he married Françoise de Lorraine, Duchesse de Mercoeur et de Penthièvre (d. 1669), the wealthy heiress of Philippe Emmanuel, Duke of Mercoeur. The couple had three children:
*Louis II, duc de Vendôme (1612–1669)
*François, duc de Beaufort (1616–1669)
*Elisabeth, Mlle de Vendôme (Paris, August 1614 – Paris, 19 May 1664), married in Paris on 11 July 1643 Charles Amédée, Duc de Nemours.

César spent much of his life intriguing against Marie de' Medici and then his half-brother Louis XIII of France. Implicated in the conspiracy of Chalais against Cardinal Richelieu, he and his brother Alexandre, the Chevalier de Vendôme, were imprisoned in the Château de Vincennes in 1626. He was released in 1630 and exiled to Holland.

In 1632, he returned to France and took part in the "cabale des Importants" against Cardinal Mazarin with his second son François. Exiled again, this time to England, he did not return until 1642. The marriage of his son Louis to Laura Mancini brought about his reconciliation with Mazarin, and he supported Anne of Austria throughout the Fronde. In 1651, he was appointed Admiral of France, and Grand Master of Navigation in 1655.

He was the head and founder of the House of Bourbon-Vendôme.