Assassin's Creed calls the precursor civilization behind the Pieces of Eden the Isu.
The Isu are an advanced civilization that existed before recorded human history in the series' fictional mythology. They created powerful artifacts known as Pieces of Eden, including Apples, Swords, and the Staff of Hermes Trismegistus. These objects can influence human perception, behavior, or biology and drive much of the conflict between Assassins and Templars.
The Isu also created humans, according to the series' lore, and the two populations later fought a major war. A catastrophic solar event weakened both civilizations, after which humanity survived and the Isu declined. Later games reveal more Isu figures and sites through visions, genetic memories, and archaeological discoveries.
Older games often refer to them as the First Civilization or Those Who Came Before. Those phrases describe the same precursor people, but “Isu” is the specific name used prominently in later canon and reference material.