Ok, did a little bit of research because I know how the folks at Ubisoft used real people who were had died as the targets in Assassin's Creed 1. This is what I found about a certain Duke of Milan who died in 1476:
There were three principal assassins involved in Sforza's death: Carlo Visconti, Gerolamo Olgiati and Giovanni Andrea Lampugnani, all fairly high-ranking officials in the Milan court.
Lampugnani, descended from Milanese nobility is recognized as the leader of the conspiracy, his motives based primarily on a land dispute, in which Galeazzo failed to intervene in a matter which saw the Lampugnani family lose considerable properties. Visconti and Olgiati also bore the duke enmity - Olgiati was a Republican idealist, whereas Visconti believed Sforza to have taken his sister's virginity.
After carefully studying Sforza's movements, the conspirators made their move on the day after Christmas, 1476, the official day of Santo Stefano, the namesake of the church where the deed was to be committed. Supported by about thirty friends, the three men waited in the church for the duke to arrive for mass. When he arrived, Lampugnani knelt before him, and after some words were exchanged, rose suddenly, stabbing him in the groin and breast. Olgiati and Visconti soon joined in, as did a servant of Lampugnani's.
Sforza was dead within a matter of seconds, and all the assassins quickly escaped the ensuing mayhem, save for Lampugnani, who became entangled in some of the church's cloth and was killed. His body soon fell into the hands of a mob, which dragged it through the streets, slashing and beating at it and in the end, hanging it upside-down outside his house. The beheaded corpse was cut down the next day and, in an act of symbolism, the "sinning" right hand was removed, burnt and put on display.
And, just for reference, this particular duke was NOT a nice man:
Despite his love of music, Sforza is also known to have had a cruel streak. He was a notorious womanizer who often passed his women on to his courtiers once he tired of them. He once had a poacher executed by forcing him to swallow an entire hare (with fur intact), had another man nailed alive to his coffin, and a priest who had predicted a short reign was punished by being starved to death. This made him many enemies in Milan. It was also said of Sforza that he had raped the wives and daughters of numerous Milanese nobles; that he took sadistic pleasure in devising tortures for men who had offended him and that he enjoyed in pulling apart the limbs of his enemies with his own hands.
and just to be to quote my source.
http://en.wikipedia.org/wiki/Galeazzo_Maria_Sforza