Which artifact is central to the plot of the first Assassin's Creed game?

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

In the game, the Apple is a Piece of Eden, an ancient Isu artifact with powerful abilities that can influence human perception and behavior. Altaïr seeks it during the Third Crusade, and its possession becomes a major reason for the conflict among the Assassins, Templars, and their allies.

The Apple also connects the historical storyline to Desmond Miles's modern-day narrative. The Animus allows Desmond to experience Altaïr's memories, while the Templars' interest in the artifact shows that the ancient struggle has continued into the present.

The series contains many Pieces of Eden, so the names are easy to mix up. The Staff of Hermes is prominent in Odyssey, the Shroud of Eden appears in Syndicate, and the Sword of Eden is associated with later Templar history. The first game's specific artifact is the Apple.