The Animus lets Desmond Miles relive ancestral memories in Assassin's Creed.
In the series' modern-day story, the Animus is a machine developed by Abstergo Industries. It allows a user to access genetic memories inherited from ancestors and experience them as interactive simulations. Desmond uses it to explore the lives of Altaïr Ibn-La'Ahad and Ezio Auditore da Firenze.
The device explains how the games can move between modern laboratories and historical periods without treating time travel as the mechanism. Desmond remains in the present while the Animus reconstructs experiences from his ancestry.
Players sometimes confuse the Animus with the Helix. The Helix is a later Abstergo entertainment system, while the Animus is the broader technology and the name most strongly associated with the early games.