The trilogy is set in a distant future in which humanity has joined a wider galactic community after discovering technology left behind by an ancient, vanished civilization. Playing as Commander Shepard, a soldier in the human military, the player is named the first human agent of an elite galactic order and sent to investigate an attack tied to a rogue operative. The investigation reveals a far larger threat: the Reapers, a race of ancient machines that periodically returns to wipe out advanced life across the galaxy. Across the three games, Shepard assembles a team and works to rally the galaxy's civilizations against this looming danger.