The famous precursor artifact often called the Apple in Assassin’s Creed is the Apple of Eden.
The Apple of Eden is one of the Pieces of Eden, advanced artifacts created by the Isu, an earlier civilization in the series’ mythology. It can influence minds and project or manipulate information, making it valuable to both Assassins and Templars. Different games show different Apples and related effects.
The artifact is not the same as a conventional magical apple from a religious or fairy-tale story. Assassin’s Creed uses familiar historical and mythological imagery while explaining it through its fictional Isu civilization and science-fiction framework.
Other Pieces of Eden include the Staff, Sword, Shroud, and observatory-related devices. The Apple remains the best-known example because it appears prominently in the first game and several later stories. Its exact capabilities vary somewhat between installments, but its strategic importance is consistent.