What artifact is central to the plot of the original Assassin's Creed?

The artifact central to the plot of the original Assassin's Creed is the Apple of Eden.

The Apple is one of the Pieces of Eden, powerful technological artifacts created by the Isu, an advanced civilization that existed before recorded human history in the series’ mythology. The Templars seek these objects because they believe they can impose order and control over humanity.

In the first game, Altaïr encounters an Apple during his missions and discovers that it can produce extraordinary effects, including illusions and control over people. Its existence helps connect the medieval storyline to the modern-day conflict involving Abstergo Industries.

Other Pieces of Eden appear throughout the franchise. The Sword of Eden and Shroud of Eden are separate artifacts, so they are not interchangeable names for the Apple. The Apple is often depicted as a small golden sphere, although multiple Apples exist within the series’ wider lore.