The Isu are the ancient precursor civilization in the Assassin's Creed video-game series.
The Isu, also called the First Civilization or Those Who Came Before, existed long before recorded human history. They created powerful artifacts known as Pieces of Eden and engineered humanity for labor. Their disappearance and the survival of their technology shape the series' modern and historical storylines.
Important Isu figures include Minerva, Juno, and Jupiter. Their messages reach later characters through artifacts, temples, simulations, and genetic memories. The Great Catastrophe, a solar event, devastated their civilization and helped create the conditions for human independence.
The Isu are not the same as the Templars, Abstergo, or the Hidden Ones. The Templars are a human ideological order, Abstergo is a modern corporation connected to them, and the Hidden Ones are the ancient predecessors of the Assassins. These groups interact with Isu technology but are not the precursor civilization itself.