Of all of the protagonists in the Assassin's Creed franchise, none are as fleshed out as Ezio Auditore da Firenze. From his birth to his death, the developers at Ubisoft left no stone unturned regarding his story. However, while most of his installments are considered hits, the least talked about has become the series' most important. Assassin's Creed: Revelations follows the latter years of Ezio's life. While the story doesn't have a larger impact on the overarching narrative, it finally answers why the assassins are so important to the world.
After Ezio eliminated the Borgia threat from Rome and sought justice for the murder of his father, uncle and brothers, he spent his middle-aged life learning. From one of his father's notes, he learned of a secret library in the old headquarters of the Assassins during the time of Altaïr Ibn-La'Ahad. With its location known, Ezio ventured to Masyaf to find this library and began a treasure hunt unlike anything seen in the franchise at that time.
Altaïr is the first assassin in the franchise, which began in 2007. Before his reappearance in Revelations, his story never concluded and the rest of his life was a mystery. Through Ezio, players can experience Altaïr's most personal memories over the many decades of his life. Altaïr's experiences also defined the importance of the Assassin Brotherhood in a way that wasn't explained before.
Through Ezio's journey, there is an understanding that since the Templar Order seeks power and knowledge to control humanity, it is the Assassin's duty to deny them the opportunity. However, Revelations shows that their methods go far beyond striking from the shadows. Assassins are meant to safeguard the knowledge that Templars would use for conquest.
By being preservers of knowledge, assassins devote themselves to a higher cause that may one day ask for the ultimate sacrifice. During the earlier titles, the most important artifact in the series was the Apple of Eden. The Apple allowed the user to control those around them. Aware of the inherent danger and after a betrayal by Altaïr's mentor, Al Mualim, the elderly assassin chose to lock himself away with the Apple in Masyaf's secret library. There he died, preserving the knowledge that came before him.
Even in his later years, Ezio still had much to learn. Finding Altaïr's skeleton in the library serves as a lesson to Ezio and all others who join the Assassins. The goal of the Assassins is to safeguard knowledge from those who would seek to abuse it, no matter the cost. Revelations is a game that shows the impact knowledge has and why the assassins continue to fight after centuries of endless conflict. Though it isn't the most popular game, Assassin's Creed: Revelations is still the only title to show why the Assassin Brotherhood is integral to the world.