The Isu are the fictional precursor civilization featured throughout the Assassin's Creed series.
The Isu are an ancient, technologically advanced species that existed before recorded human history in the series' mythology. They created humans as a labor force and produced powerful artifacts, including the Pieces of Eden. Their civilization was devastated by a solar event, after which humanity became the dominant species.
The Isu are also called the First Civilization in much of the franchise's terminology. They remain important even when they are not physically present because their technology drives conflicts in both the historical and modern-day narratives. Characters such as Minerva, Juno, and Jupiter are associated with the Isu storyline and appear through messages, simulations, or reconstructed memories.
The Templars and the Hidden Ones are human organizations, so they are not the answer. The Hidden Ones are precursors to the Assassin Brotherhood, while the Templars pursue control through their own historical order. “First Civilization” is a recognized descriptive term for the Isu, but “Isu” is the specific name requested here.