The precursor civilization in the Assassin’s Creed series is called the Isu.
The Isu are an ancient, highly advanced species that existed before recorded human history in the series’ fictional mythology. They created humanity and developed powerful technologies, including the Pieces of Eden. Their civilization was devastated by a solar catastrophe, after which humans survived and eventually became the dominant species.
The Isu were originally often described in the games and reference material as the First Civilization or Those Who Came Before. “Isu” became the standard name used in later series storytelling and encyclopedic descriptions. Important Isu figures include Minerva, Juno, and Jupiter, who influence the modern-day plot through messages and preserved artifacts.
The Isu should not be confused with the Templars or Assassins. Those are human factions that emerge much later. The Templars seek control and order, while the Assassins defend human freedom; both groups interact with Isu technology and history.