In Assassin's Creed lore, the Isu created the Apple of Eden.
The Isu are an advanced precursor civilization that existed on Earth before modern humans. Their technology includes powerful Pieces of Eden, among them the Apple, which can influence human perception and behavior through its electromagnetic and neural capabilities.
The Apples are not ordinary fruit. They are spherical artifacts used by Isu and later sought by both the Templars and the Assassins. Different games depict Apples in various historical periods, where their power becomes part of conflicts involving rulers, religious institutions, and secret organizations.
The Isu are also called the First Civilization in much of the series. The Templars did not create the Apples; they pursue and exploit them. The Hidden Ones and later Assassins generally try to keep such artifacts from being used for domination.