The Isu are the fictional First Civilization in Assassin's Creed lore.
The Isu are an ancient, highly advanced species who existed before recorded human history in the series' fictional mythology. They created humanity and powerful artifacts known as Pieces of Eden, including objects that can influence human perception and behavior. Their civilization was devastated by a global catastrophe associated with solar activity, after which humans became the dominant species.
Earlier games often referred to the Isu as the Those Who Came Before or the Precursors. Those terms describe the same broad civilization and can create confusion when reading older summaries of the series. The name Isu became increasingly prominent in later lore and modern descriptions.
The Isu are not the same as the Templars or the Assassins. The Templars and Assassins are human organizations that emerge much later and interpret the legacy of Isu technology in opposing ways. Isu figures, memories, and artifacts appear throughout the franchise, linking its historical adventures to its science-fiction storyline.