In Assassin's Creed, the fictional historical order opposed to the Assassins is the Templar Order.
The series presents the Assassins and Templars as rival secret societies whose conflict stretches across many periods of history. The Assassins generally seek human freedom and resistance to imposed control, while the Templars pursue peace through order, authority, and centralized power.
The games use real historical settings but turn the rivalry into an alternate-history framework. Figures and institutions inspired by history appear alongside fictional characters, artifacts, and conspiracies. In the modern-day storyline, Abstergo Industries serves as a contemporary continuation of the Templar cause.
The Templars should not be confused with every historical knightly group shown in the games. The Knights Templar were a real medieval military order, but the franchise's Templar Order is a fictional organization that extends far beyond the real order's existence.