The Apple of Eden is the fictional artifact that can let its holder control minds in Assassin's Creed.
An Apple of Eden is one of the series' Pieces of Eden, advanced artifacts created by the Isu, an ancient civilization that existed before humanity's recorded history. The Apples are associated with powerful effects including illusions, influence over human behavior, and the control of minds. Their power makes them central objects in the conflict between Assassins and Templars.
The artifacts are inspired in part by the biblical story of the forbidden fruit, but the series gives them a science-fiction explanation rather than treating them as literal religious objects. Different games show different Apples and different uses, so the term refers to a class of artifacts rather than one single prop that remains in every installment.
Other Pieces of Eden include the Staff, Sword, Shroud, and crystal skulls. The Spear of Leonidas and Staff of Hermes are important artifacts in individual games, but they are not the canonical name for the mind-influencing Apple.