Assassin's Creed calls the ancient precursor civilization behind its artifacts the Isu.
The Isu are an advanced civilization that existed on Earth before modern humans became dominant. In earlier games they were often called the First Civilization, Those Who Came Before, or the Precursors, but “Isu” became the principal canonical name in later lore.
The Isu created powerful Pieces of Eden, including the Apple of Eden, and used them in their interactions with humanity. Their civilization was devastated by a solar event, although individual Isu figures and their recorded consciousnesses continue to influence the series' modern and historical plots.
The Isu should not be confused with the Assassins or Templars. Those two human factions debate freedom and control, while the Isu belong to a much older civilization whose technology is frequently mistaken for magic. Characters such as Minerva, Juno, and Aita are connected to Isu history.