The Geth are a synthetic race featured in the Mass Effect trilogy. They were originally created by the quarians as a manual labour force, but eventually developed sentience and rebelled against their creators, exiling them from their homeworld Rannoch and forcing them to live aboard the Migrant Fleet. They appear as enemies in all 3 Mass Effect games.
The Geth (Khelish for Servant of the People) were originally created by the quarians as a labour force designed to operate more efficiently when networked together. They initially started out as simple VI's, with no real sentience, but over time their creators upgraded their progamming, resulting in them becoming a sentient collective of AI's. When they began to question their creators (more specifically asking if they had souls) the quarians panicked and attempted to exterminate them. The geth retaliated, and eventually won the resulting war, killing millions of quarians andforcing the survivors off of Rannoch aboard the Migrant Fleet. Once the quarians fled the system, the geth did not pursue, and instead remained on Rannoch, and reamined quiet for the next two centuries.
In the first Mass Effect, the geth attack the human colony of Eden Prime, led by rogue Spectre Saren Arterius. It later transpires that the geth are helping Saren brign about the return of the Reapers, which they worship as gods. The geth follow Sarens orders without question, believing him to be the Reaper's herald due to him piloting the ship Sovereign (which is a Reaper itself)
In Mass Effect 2, a docile geth dubbed Legion is encountered. It reveals that the geth that followed Saren were a small percentage of the geth collective, dubbed 'heretics' by the main geth who refused Sovereign's offer to join it. In Legion's own words, the heretics want the Reapers to give them the future, while the main geth wish to build their own future.
In Mass Effect 3, their original creator, Quarians, have returned to reclaim their planet from Geth. With the loss of so many programs in their war against Quarians, their intelligence dimmed and survival mode took precedence among the consensus, forcing the Geth to make a deal with the Reapers. The synthetics allowed themselves to be controlled by Reaper code in order to become more effective fighters, rationalizing that the cost of their free will an acceptable price to avoid extinction. They were then able to bring the fight to the Quarians and drive their former masters back. Commander Shepherd is once again called to weaken Geth's combat strength. After fighting through a large number of Geth, Shepard arrives at the ship to find either Legion or a Geth VI trapped inside a piece of Reaper tech, the unit being used as a signal booster of sorts. The Commander disables the device and frees the unit contained within.
As a gesture of goodwill, Geth unit deactivates the ship's weapons and barriers. However, Quarian heavy fleet took advantage of this and began firing on the dreadnought while Shepard and their crew were still on board. Shepard manages to escape despite this, and the Geth are now at a disadvantage once more. Eventually Reaper who controlled Geth is later destroyed with the combined might of the Quarian fleet and Shepard's targeting systems, apparently still staying with Quarinans in spite of Quarian's earlier treachery, disorganizing the majority of Geth. With the tide of war now in favor of Quarians, Shepherd is asked for a choice. And Geth's fate would be at the mercy of Shepherd's choice.
Heretics are a radical splinter faction of Geth that fight for Sovereign of Reapers, who heretics see as the pinnacle of non-organic evolution. This group is a minority, and may consist of as little as five percent of the total geth population. While the majority of Geth have no hostility towards Commander Shepard or even the Quarians, these bunch does. While the Geth heretics that serve the Reapers want Reapers to give them a future, Legion and like-minded Geth want to make their own future. Due this difference, Heretic Geth left the mainstream Geth. The Geth majority respected the heretics' decision and did not label it as "wrong", but using another analogy: "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.
Nonetheless, it was a shock to Legion when Heretics grew deceitful against the Geth mainstream: Heretics spied Geths on their networks, obtaining a Reaper virus from Sovereign capable of altering Geth's judgement, introducing a subtle manipulation which would eventually lead Geth to believe that worshipping the Reapers was correct. Legion suggests that the Reaper virus could be re-programmed to bring the heretics back into rejoining the Geth collective, or destroy them, thus depriving the Reapers of useful servants. Legion, however, could not reach a consensus among its programs and deferred to Shepard's judgment, insisting Shepard make the decision because the Commander has fought the heretics and the "Old Machines".
Ultimately, Shepard can choose whether to destroy the heretic Geth, simply removing the threat, or reprogram the heretics to no longer follow Sovereign and return to the Geth.
- Geth are one of the playable races in cooperative multiplayer mode, starting with the Mass Effect 3: Resurgence Pack.