The fictional precursor species in the Assassin's Creed series is called the Isu.
The Isu are an advanced civilization that existed before recorded human history in the series' fictional universe. They created humans and developed powerful artifacts, including the Pieces of Eden, which drive many conflicts between Assassins and Templars.
Earlier games often referred to individual Isu as the “Those Who Came Before,” and some were identified through names from human mythology, such as Minerva, Juno, and Jupiter. Later stories use “Isu” as the broader species name.
The Isu are not the same as the Assassins or Templars. The Assassins and Templars are human ideological factions, while the Isu belong to an earlier civilization. The series uses their remnants to blend historical adventure with science fiction and questions about free will, control, and inherited memory.