The Animus lets Desmond Miles relive his ancestors’ memories in the original Assassin’s Creed.
The device is a machine developed by Abstergo Industries, the modern-day organization controlled by Templars. Desmond is placed inside it so Abstergo can access the genetic memories of his ancestor Altaïr Ibn-La’Ahad, whose life provides most of the game’s historical gameplay.
The Animus is not a time machine. It reconstructs inherited memories encoded in a person’s DNA, allowing the user to experience an ancestor’s perspective. The concept supplies the series with its transitions between modern-day scenes and historical settings.
The Apple of Eden is a separate Isu artifact, while the Bleeding Effect is a consequence of prolonged Animus exposure. The Codex is a collection of writings associated with Ezio’s storyline, not a device used by Desmond.