The Isu are the fictional precursor race in Assassin's Creed lore that created the Pieces of Eden. They are an advanced civilization that existed before recorded human history and are also called the First Civilization in the series.
The Isu created powerful artifacts, including the Apple of Eden, the Staff of Hermes, and other Pieces of Eden. Humans were created or modified by the Isu and were once controlled by them, but the human uprising and a catastrophic solar event changed the balance between the two species.
“The First Civilization” is a recognized description of the Isu, but it is not the name requested here. “Precursors” is a broad label sometimes used in discussions of fictional ancient civilizations, while “the Ancients” is associated with factions in particular games. The Isu appear across the modern-day mythology of the franchise.