The Templars are the Assassins' main fictional enemy throughout Assassin's Creed.
In the series, the Assassins and Templars represent opposing philosophies. Assassins generally defend free will and resist centralized control, while the Templars seek peace and order through authority, planning, and control. Their conflict continues across different historical periods, with names and institutions changing over time.
The Templars are not presented as a simple copy of the historical medieval order. Assassin's Creed uses the real Knights Templar as inspiration but builds a secret organization that survives and evolves across centuries. In the modern storyline, Abstergo Industries serves as a major Templar-controlled corporation.
The Hidden Ones are the ancient Egyptian organization that later becomes the Assassin Brotherhood. The Order of the Ancients is an earlier enemy network featured in Origins, while Abstergo's council is a modern internal body. These groups are related to the wider mythology but are not the franchise's general name for the opposing faction.