In the Assassin's Creed series, the Templars are the organization that opposes the Assassins across the historical storylines.
The Templars generally seek order and control, while the Assassins defend human freedom and individual choice. The series presents this conflict through different historical eras, with both organizations changing names, methods, and leaders over time. Their rivalry is the central fictional struggle connecting otherwise separate protagonists.
The Templar Order is not identical to every enemy faction in every game. For example, the Cult of Kosmos is a major opposing group in Odyssey, and the Order of the Ancients appears in Origins and Valhalla. These groups are connected to the broader conflict but have distinct identities and historical contexts.
The Assassins themselves are also known as the Hidden Ones in earlier periods of the chronology. That name is especially important in Origins, which depicts the organization's formation. The Templars remain the canonical long-term opposing organization in the series' modern and historical mythology.