Charles IV, Duke of Mantua(Revere, August 31 1652 - Padua, July 5 1708) was the only child of Duke Charles III of Mantua and Montferrat, and the last ruler of this Duchy.

Charles IV first married Anna Isabella Gonzaga († August 11 1703), daughter of Duke Ferrante III Gonzaga of Guastalla. On November 8 1704 he remarried with Susanna of Lorraine (February 1 1686 - December 19 1710), daughter of Duke Charles of Elboeuf. This marriage remained childless.

Frustrated by the Austrians in taking over Guastalla, he concluded a pact with Louis XIV of France on December 8 1678, selling Casale. In this context his minister count Ercole Antonio Mattioli , could be the Man in the Iron Mask when he was imprisoned in Pinerolo in April 1679 for disclosing this pact to the enemies of France.

Gonzaga denied everything, but concluded a new pact with the French in 1681, earning himself a yearly pension of 60.000 Lire, a career as an army General and a part in any future French conquests in Italy.
The French occupied Casale on September 29, 1681.
Gonzaga lost all respect in Italy.

Charles again chose the French side in the War of Spanish Succession, but paid heavily for his choise, when the French were chased back over the Alps in 1706.
Already declared a traitor in 1701 by Austrian Emperor Joseph I, all his possesions were confiscated in 1708.

The House of Savoy got the second half of Montferrat (they had already conquered the first half in the War of the Mantuan Succession in 1631). The Duchy of Mantua became Austrian and ceased to exist.
Charles died the same year in Padua.