The son of Muzio Sforza, Francesco was originally a mercenary leader, most famous for being able to bend metal bars with his bare hands. He later proved himself to be an expert tactician and very skilled field commander. He saved the Visconti rulers of Milan from ruin on a number of occasions. As a reward, the then duke of Milan, Filippo Maria Visconti, allowed Francesco to marry his daughter Bianca, but after the duke died without a male heir, fighting broke out. During this time, Franscesco turned against the Visconti, and seized control of Milan and its possessions.
Under his rule (which was moderate and skillful), Francesco modernized the city of Milan. He created an efficient tax system that generated enormous revenues for the government, his court became a center of Renaissance learning and culture, and the people of Milan loved him.
During Sforza's reign over Milan, Florence was under the command of Cosimo de Medici and the two enlightened rulers became close friends. This friendship eventually manifested in the Peace of Lodi, an alliance between Florence and Milan that succeeded in stabilising almost all of Italy for its duration.
Francesco is mentioned several times in Machiavelli's book The Prince, he is generally praised in that work for his ability to hold his country and as a warning to a prince not to use mercenary troops.
Regretably Francesco's successors were not nearly as competent, a number of them being dangerously unbalanced individuals.