Which Assassin's Creed game introduced the Brotherhood's recruit system and the character Niccolò Machiavelli?

Assassin's Creed: Brotherhood introduced the Brotherhood's recruit system and the character Niccolò Machiavelli.

In Brotherhood, Ezio Auditore rebuilds the Assassin Brotherhood in and around Rome after the Borgia family attacks Monteriggioni. Players can recruit civilians, train them, and call them into missions. The system turns the Brotherhood from a background organization into an active strategic resource that supports Ezio in combat and investigation.

Niccolò Machiavelli appears as one of Ezio's important allies and fellow Assassins. The historical Machiavelli was a Florentine diplomat and political thinker, and the game uses his real identity within its fictionalized Renaissance plot. He helps Ezio oppose Cesare Borgia's influence in Rome.

Assassin's Creed II established Ezio's origin, while Revelations continued his story in Constantinople. Brotherhood was released in 2010 and also introduced the series' first major competitive multiplayer mode, alongside its single-player campaign.