The Isu are the ancient civilization also called the First Civilization in Assassin's Creed lore.
The Isu are portrayed as an advanced species that existed before modern humans and created powerful Pieces of Eden, including the Apple of Eden. Their civilization shaped humanity's origins and the long-running conflict later inherited by the Assassins and Templars.
The games reveal Isu history gradually through artifacts, genetic memories, holographic messages, and simulations. They are sometimes loosely described as gods because ancient human cultures remembered them through myth, but the series presents them as a technologically advanced civilization rather than supernatural deities. The term Precursors is another label used for the same civilization.