Gian Galeazzo Sforza (also Giovan Galeazzo Sforza) (20 June 1469 - 21 October 1494) was the sixth Duke of Milan.
Born in Abbiategrasso, he was only 7 years old when in 1476 his father, Galeazzo Maria Sforza, was assassinated and Gian Galeazzo became the Duke of Milan. His uncle, Ludovico Sforza, acted as regent to the young duke but quickly wrestled all power from him and became the de facto ruler of Milan for some time. In 1488, Gian Galeazzo married his cousin princess Isabella of Naples and they had three children together: Ippolita Maria Sforza (1490-1501), Francesco (1491-1512), Bona (1494-1557) (who married Sigismund I of Poland) and Bianca Maria (1495-1496).
Concerning Gian Galeazzo's death in 1494 (Pavia), Italian historian Francesco Guicciardini had this to say in his La Historia di Italia (The History of Italy):
The rumor was widespread that Giovan Galeazzo's death had been provoked by immoderate coitus; nevertheless, it was widely believed throughout Italy that he had died not through natural illness nor as a result of incontinence, but had been poisoned... one of the royal physicians...asserted that he had seen manifest signs of it. Nor was there anyone who doubted that if it had been poison, it had been administered through his uncle's Ludovico Sforza machinations...