Having taken power from the Republic of Florence after being elected as a supposed figurehead, he restored the power of the Medici, who thereafter ruled Florence until the last of the Medici Grand Dukes, Gian Gastone de' Medici (1671-1737). The governmental structures he set up endured past that, when it was absorbed into the Austro-Hungarian Empire.
Among his many accomplishments were the creation of the Uffizi, originally intended to house the government, and now one of the world's great art galleries; the creation of the Florentine navy, which played a key role at the battle of Lepanto; the expansion of Florence to control most of Tuscany, including Siena; taking over the Pitti Palace as a home for the Medici and finishing it off; the creation of the magnificent Boboli Gardens behind the Pitti; the promotion of the University of Pisa; and a host of other accomplishments in the economic, architectural and artistic spheres, including supporting Vasari and Cellini.
A large equestrian statue of him in bronze, by Giambologna, erected in 1598, still stands today in the Piazza della Signoria, the main square of Florence.
Cosimo's son, Francesco I (1541-1587) was an ineffectual ruler under whom Tuscany languished.
Cosimo's son, Ferdinand II (1610-1670) was just ten years old when he became Grand Duke, and until his majority the government was carried on by the two Grand Duchesses, Cosimo's mother Christina of Lorraine, and Cosimo's wife, Maria Magdalena of Austria, the sister of the Holy Roman Emperor Ferdinand II.
Cosimo II's wife, Maria Magdalena, was the sister of Ferdinand II, Holy Roman Emperor.
In 1433 Cosimo was exiled from Florence by Rinaldo degli Albizzi, but public opinion soon changed, and he returned in 1434, to greatly influence the government of Florence and to lead by example for the rest of his long life.
Cosimo was also noted for his patronage of culture and the arts, liberally spending the family fortune (which his astute business sense considerably increased) to enrich Florence.
In the Constance Concilium Cosimo through his older son, Lorenzo de' Medici tried the political survival of the cismatic pope John XXIII by trying to influence the decisions of the Concilium in favour of John XXIII.