Cosimo I de' Medici (1519–1574) was the Duke of Florence from 1537 until 1569, when he became the first Grand Duke of Tuscany. Part of the junior branch of the Medici dynasty, Cosimo came to power after the assassination of Alessandro de' Medici marked the end of the senior branch's rule. Although several hoped to rule through the 17-year-old Cosimo, he proved strong-willed, astute and ambitious. Over time, he established himself as an authoritarian ruler who backed the military while simultaneously serving as a lavish patron of the arts. His descendants ruled Florence for much of two centuries, ending with the death of Gian Gastone de' Medici in 1737.Painting: Bronzino