The Isu are the precursor civilization that includes Juno and Minerva in Assassin's Creed lore.
The Isu are an advanced species that existed before recorded human history. They created humanity and produced powerful artifacts, including the Pieces of Eden. Their civilization was devastated by a catastrophic solar event, after which surviving Isu and human societies shaped the mythology and history explored by the games.
The series initially referred to them mainly as the First Civilization. Later entries established Isu as the name most commonly used for the species and civilization. Important Isu figures include Minerva, Juno, Jupiter, and Aita, although their roles and appearances differ across games.
The Isu are not the same as the Templars. The Templars are a human organization, while the Isu belong to the much older precursor civilization that created many artifacts central to the modern conspiracy.