The memory-simulation device in Assassin's Creed is called the Animus. It allows a person in the present to access genetic memories inherited from ancestors.
In the first game, Desmond Miles is forced to use an Animus by the Templar-controlled company Abstergo Industries. By reliving Altaïr's memories, he helps Abstergo search for the locations of powerful Pieces of Eden.
The Animus provides the series with its modern-day framework while allowing the main action to occur in historical periods. Later stories introduce related systems, including the Helix entertainment platform and portable or modified Animus technology.