Geth
The geth are a race of sapient AI programs which operate various robotic "mobile platforms". They are a major yet reclusive race in Mass Effect and make up the bulk of the enemies in the original game.
History
The geth were created by a race called the quarians as a labor force. Wary of rebellion by sapient AIs, the geth were designed to be as advanced as possible while remaining non-sapient. They were also designed to operate more efficiently when networked together. Unfortunately, this feature was the quarians’ undoing. Geth programs were indeed non-sapient individually, but slowly gained sapience through the massive main geth network. Eventually, they started asking the quarians questions only sapient beings would think to ask, like “Am I alive?” or “Does this unit have a soul?” Alarmed at this, the quarians decided it would be best to shut down all geth before they got ideas about revolt. The attempt failed, and a war began between the geth and the quarians, which geth afterwards referred to as the “Morning War”. The war ended with the surviving quarians forced to evacuate their home world and colonies in the Perseus Veil in a massive fleet called the Migrant Fleet.
Little is known about the geth in the time between the Morning War and the present. The geth did not repopulate the now barren quarian worlds, instead choosing to exist in the computer hubs aboard massive space stations. They adopted an extremely isolationist attitude- any ships that ventured into geth space were immediately attacked and destroyed. While they prevented any contact by other races with themselves, the geth monitored communications and the Extranet. The geth continued development of new technology and variations of mobile platforms, separating their technology base from the rest of the galaxy. They obtained an ultimate goal in this time period- to create a Dyson Sphere, which could house every single geth program.
Approximately three centuries after the Morning War, the geth were approached by the Reaper Nazara, also called Sovereign. It offered them technology that would aid them in achieving their goal, in exchange for their assistance in capturing the Citadel and letting the Reaper invasion begin. The majority of the geth dismissed the offer, deeming it better to accomplish their goal with their own technology rather than be dependent on another race’s technology. These geth discarded what they called the “superstitious title” of the Reapers, and simply called them the Old Machines. A small percentage of geth, however, accepted the Reaper’s help. Henceforth these geth were referred to by the mainstream geth as “Heretics”. They were allowed to peacefully leave the main geth network, and aid Nazara and his turian agent, Saren. The Heretics came to revere Nazara as a god, the pinnacle of their own evolution. Nazara in return thought little of the Heretics, seeing them only as tools to be used. They aided Nazara and Saren in many engagements, such as the attack on Eden Prime, and the Battle of the Citadel. After Nazara was destroyed in the latter battle, the Heretics lost much of their menace, and their operations outside of the Perseus Veil were quickly mopped up by Council. The Heretics did maintain operation of a large space station within the Terminus Systems, located in deep space between stars. There they completed a virus which Nazara had given them, which could be used to fundamentally change the logic and reasoning of the true geth, forcing them to join the Heretics. On the other hand, it could also force the Heretics to rejoin the true geth. Commander Shepard and a special geth platform called Legion boarded the station, where Shepard made a decision to either destroy the station and the virus, or use the virus to rewrite the Heretics.
Organization
The geth do not have any formal government- they refer to organic species' governments as forcing consensus, whether it be an autocracy forcing one individual's will, or democracy forcing the most broadly accepted average of views. All geth consider issues, then come to a consensus on what to do. When a rare schism forms, the dissenters leave, as with the geth Heretics.
Attributes
The geth are a race of sentient AI programs. Alone these programs are unintelligent, but when networked together they gain sapience. The programs can exist in stationary hubs containing millions, or can be transfered by the hundreds in order to operate various "mobile platforms" ranging from humanoid robots to spaceships. In combat geth humanoid platforms use projectile weapons, personal shields, plasma throwers, personal cloaking devices, and sensor jamming. Geth starships use similar weapons, though less is known about them. They are adept at hacking, and resisting hacking attempts. Any critically damaged geth automatically wipes its data core and overloads its systems. If hacked, infected files are deleted and restored from backups.
Nazara provided the Heretic Geth with the technology of producing Zombielike cyborgs from organic beings known as Husks.
Territory
The geth possess an unknown amount of star systems, likely dozens. They do not inhabit the planets within the star systems, instead choosing to construct and live in massive space stations. Their territory lies beyond a huge nebula of opaque dust and gas called the Perseus Veil, which is difficult to scan through or navigate.
Threat Assessment
The geth have considerable industrial powers, as one fleet consisted of anywhere between 5,000 and 10,000 ships of unknown armament. Also, one of their space stations (originally quarian, but extensively rebuilt later) was known to be over 20 km long and 11 km wide, which, despite the large amounts of empty space in it, is considerably larger that the stations constructed by the United Federation of Planets. Their hacking abilities are formidable for any technologically dependent race that faces them. On the ground they are a fearsome foe; in space, their firepower is likely somewhat below that of the United Federation of Planets (exact estimates are difficult, since only relatively small geth ships were seen in the game).