Duke of Mantua from 1550 to 1587, and of Montferrat from 1574 to 1587. He was the second son of Federico II Gonzaga, Duke of Mantua and Margaret Palaeologina of Montferrat. In 1574, Montferrat was elevated to a Duchy and Guglielmo became its first duke. He was succeeded as Duke of both duchies by his son Vincenzo.
Size 16 x 27 cms