The Isu are the ancient First Civilization race in the Assassin's Creed universe.
The Isu are a technologically advanced species that existed before modern humans and created many powerful artifacts, including Pieces of Eden. Their civilization eventually collapsed after a catastrophic solar flare, although individual Isu figures and their influence remain important throughout the series.
The term “First Civilization” describes the same ancient people in much of the series' lore. They are sometimes mistakenly called Templars because both groups are linked to the pursuit of control, but the Templars are a later human organization. The Hidden Ones are the ancient Egyptian predecessors of the Assassins, and Sages are humans connected to recurring genetic memories of Aita.
Important Isu characters include Minerva, Juno, and Jupiter. Their surviving technology and messages shape the modern conflict and explain why Assassins and Templars repeatedly seek certain artifacts.