The Isu are the fictional precursor species whose artifacts drive the Assassin's Creed series.
The Isu are an advanced civilization that existed before recorded human history in the series' mythology. They created humans and made powerful artifacts known as Pieces of Eden, including the Apple of Eden. These objects can influence minds, create illusions, or perform other extraordinary functions, and they remain central to conflicts between Assassins and Templars.
The Isu are also called the First Civilization in much of the franchise's lore. Their civilization was devastated by a catastrophic solar event, although some individuals survived or preserved their consciousness through advanced technology. Later stories reveal more about figures such as Minerva, Juno, and Jupiter.
“Templars” and “Hidden Ones” are human organizations, not the precursor species. The name Isu is the concise term used in later games and modern franchise discussions, while First Civilization is a descriptive alternate designation for the same ancient population.