Ignazio Busoni was the director of Museo dell’Opera del Duomo and thus he supervised Il Duomo, Florence's most caracteristic monument. All Florence called him by his nickname Il Duomino, the little dome in Italian, which was a reference to Il Duomo (the most famous cathedral of the city), and the fact that the man had a red face and weighed nearly four hundred pounds. He was a great fan of spaghetti Bolognese and caramel budino.
Before the beginning of Inferno, Robert Langdon scheduled a meeting with Ignazio Busoni to enter the Palazzo Vecchio after hours so both of them could take a look at Dante Alighieri's death mask. He called Marta Alvarez to request that she let him take a guest to see it in private and she agreed. While they were all at the room, Marta had to leave for the restroom and Ignazio took the oportunity to watch the corridor while Langdon stole the mask. They left quietly, but got separated just outside the museum with Ignazio holding the mask.
Ignazio knew that there were people after him who wanted to steal the mask from them so he hid it at Baptistry of San Giovanni. Then, he called his own office, instructed his secretary to find Langdon and left him an encrypted message: “Robert, listen carefully. What you seek is safely hidden. The gates are open to you, but you must hurry. Paradise Twenty-five. Godspeed.”
Later that night, he died of a heart attack and, although Langdon read the news of his death on the seventh chapter fo the novel, Ignazio's name had not yet been released so he didn't know his friend had died until Marta called his office to confront him after finding out that both of them had stolen the mask.