Galeazzo Maria Sforza (1444 - 1476) was the duke of Milan, husband of Lucreca Landriani, and father of Caterina Sforza, who would later become the countess of Forlì and Imola.
Biography
In 1476, the cities of Milan and Florence declared an alliance, thereby strengthening each other. The alliance had a negative impact on the Templars as they were conspiring to take the city of Florence. Aware of the fact that Sforza's death would weaken, at least temporarily, Lorenzo de' Medici's hold on his city, they brought up a plan to murder him.
During the same time in Florence, Giovanni Auditore and Lorenzo de' Medici were hearing rumors about an upheaval in Milan.
Lorenzo then sent his fellow assassin to investigate. Giovanni attacked a group of Templars led by Rodrigo Borgia one night. Borgia fled, but Giovanni could keep one of the Templars alive. Lorenzo's men tortured him, and under the pressure of pain, the Templar finally revealed their plan:
On the 26th of December, the day of Santo Stefano in Milan, Sforza would go in the city's greatest church to attend at the mass. Three Templars, Carlo Visconti, Gerolamo Olgiati and Giovanni Lampugnani were chosen one to murder the duke. On the 26th of December, Giovanni Auditore traveled to Milan and entered the church during mass. He then saw Lampugnani kneeling before Sforza and kissing his hand.
Giovanni tried to cross the crowd to reach them but he couldn't save the duke, as Lampugnani suddenly rose and stabbed his chest. The two others then joined him as a dozen of their armed allies fought Sforza's bodyguards and Giovanni. Visconti and Olgiati, having stabbed their enemy to death then fled. Lampugnani started running too as Sforza's Moorish bodyguard came after him. He ended up trapped in a cul de sac, and was killed by the bodyguard when Giovanni tried to convince him otherwise. Giovanni had failed to save the duke, and thus the plan was a success.