The geth ("Servant of the People" in Khelish) are a race of networked artificial intelligences that reside beyond the Perseus Veil. The geth were created by the quarians as laborers and tools of war. When the geth became sentient and began to question their masters, the quarians attempted to exterminate them. The geth won the resulting war, and reduced the quarians to a race of nomads. The history of the geth's creation and evolution serves as a warning to the rest of the galaxy of the potential dangers of artificial intelligence and to the legally enforced, systematic repression of artificial intelligences throughout galactic society.
According to Legion, the geth that served Sovereign were actually a splinter faction, and the much larger geth collective opposes the Reapers. Legion is part of this larger faction; they refer to the Reapers as "Old Machines" and Sovereign as Nazara. Legion explains that other geth have no hostility towards Commander Shepard or even the quarians. While the geth heretics that serve the Reapers want the Reapers to give them a future, Legion and like-minded geth want to make their own future. Despite this difference, the baseline geth respected the heretics' decision and did not label it as "wrong". Using another analogy, Legion explains that in simple terms, "Heretics say, one is less than two. Geth say, two is less than three." The heretics were allowed to leave peacefully, to join their god and its prophet.