Which historical figure appears as a major ally of Ezio in Assassin's Creed Brotherhood?

Leonardo da Vinci appears as a major ally of Ezio in Assassin's Creed Brotherhood.

Leonardo provides Ezio with inventions, intelligence, and technical support during the struggle against the Borgia family. In the game's Renaissance setting, Leonardo is forced to work for Cesare Borgia, and Ezio later helps him escape that situation. Leonardo's workshops also connect directly to missions involving siege weapons and other machines.

The character is based on the real Leonardo da Vinci, the Florentine artist, engineer, scientist, and inventor who lived from 1452 to 1519. Brotherhood takes creative liberties with his role and with the timing of events, as the series does with many historical figures.

Niccolò Machiavelli is also a major Assassin ally in Brotherhood, which makes him a plausible alternative. Columbus and Galileo are associated with broader Renaissance history but are not the game's central historical ally in the same way Leonardo is.