The Italian despot Gian Galeazzo Visconti, Duke of Milan (1351-1402), succeeded in conquering most of northern Italy in his ambitious attempt to place the entire Italian peninsula under his control.

Gian Galeazzo Visconti was born on Oct. 16, 1351. He was the only son of Galeazzo II, who ruled the family's Milanese territories jointly with his brother Bernabò. As a boy, Gian Galeazzo was plagued by a delicate constitution that caused him to spend more time with books than in sports. He spent his youth learning the art of ruling from his studies and from his father, and he remained physically timid and sedentary all his life.

Galeazzo II died on Aug. 4, 1378, bequeathing to his son his portion of the Milanese possessions. Gian Galeazzo made Pavia the base of his rule, as his father had before him. His uncle Bernabò, controlling the other half of the territory from...