What is the name of the secret society opposing the Assassins in Assassin's Creed?

The secret society opposing the Assassins in Assassin's Creed is the Templar Order.

Across the series, the Templars seek to impose peace and order through control, while the Assassins defend human freedom and independent choice. Their conflict is the central historical struggle connecting stories set in different eras and regions.

The Templars are inspired by the historical Knights Templar, a medieval Christian military order that existed from the twelfth to the fourteenth century. Assassin's Creed transforms that historical reference into a long-running fictional organization with influence extending through later institutions, including Abstergo Industries.

The Hidden Ones are the ancient Egyptian predecessors of the Assassins, not their enemies. The Brotherhood of Assassins is the opposing faction, and the Cult of Kosmos is a separate enemy organization in Assassin's Creed Odyssey. These related names are why the full term “Templar Order” matters.