What is the name of the secret society opposed to the Templars in Assassin's Creed?

The Assassins are the secret society opposed to the Templars in Assassin's Creed.

Across the main series, the Assassins seek to protect free will and resist attempts to impose absolute control. Their opponents, the Templars, generally pursue order through authority and the use of powerful artifacts connected to the Isu, an advanced predecessor civilization.

The conflict is presented through different names and organizations across history. In Assassin's Creed Origins, the early Egyptian group is called the Hidden Ones, while the Order of the Ancients is its contemporary enemy. Later stories show the Hidden Ones developing into the Assassin Brotherhood.

These related names are not interchangeable in every historical period. The broad, recurring society identified throughout the franchise is the Assassins, also called the Brotherhood in many games.