A financially cautious, self-made man, Giovanni was one of five sons of a poor widow. He got his first break from wealthy cousin Vieri, who gives him a job in the family firm, the Medici bank. Giovanni’s success with the branch in Rome leads to him taking over from Vieri to become the Capo of the Medici family.

Giovanni chooses his clients carefully. He demands loyalty, as well as profit. His gamble on an old friend, Baldassare Cossa, to support Cossa’s bid to become Pope, is a risk, but it pays off. In 1410 ex-pirate Cossa is elected Pope John XXIII, and Cossa hands over the entire Papal account to the Medici bank. Giovanni has become “God’s banker”.

When he dies, Giovanni is Godfather of 26 branches of the Medici family. They are the third richest family in Florence, to the fury of their rivals, the Albizzi. Modest to the end, Giovanni leaves only three books behind him, but he passes a dangerous legacy to his son.