Which Assassin's Creed game introduced the modern series' Animus concept through Desmond Miles?

Assassin's Creed introduced the modern series' Animus concept through Desmond Miles.

In the original 2007 game, Desmond is abducted by Abstergo Industries and forced to use the Animus, a machine that accesses ancestral memories. Through it, he experiences the life of Altaïr Ibn-La'Ahad during the Third Crusade. The modern-day storyline frames the historical action and establishes the series' science-fiction premise.

The Animus is not a conventional time machine. It reconstructs memories inherited through a person's genetic lineage, allowing the user to perceive events from an ancestor's perspective. This explanation lets the series move between historical periods while retaining a present-day narrative.

Assassin's Creed II expands Desmond's role and introduces a new ancestral subject, Ezio Auditore, but it does not introduce the concept. Origins and Odyssey take place much earlier in history and use later forms of the Animus framework. The original title therefore provides the canonical introduction.