The Borg

"Resistance Is Futile: You Will Be Assimiliated"

The Borg were a pseudo-race of cybernetic beings, or cyborgs, from the Delta Quadrant. No truly single individual existed within the Borg Collective (with the possible sole exception of the Borg Queen), as they were linked into a hive mind. Their ultimate goal was perfection through the forcible assimilation of diverse sentient species, technologies, and knowledge. As a result, they were among the most dangerous and feared races in the galaxy.

Physiology
The physiology of each Borg drone varied according to the species from which it was assimilated. (Star Trek: First Contact) Drones were typically humanoid, although the Collective has demonstrated a willingness to assimilate non-humanoid life forms. (VOY: "Scorpion")

Upon assimilation, a drone would cease to grow body hair and develop an ashen, grayish skin coloration, ignoring original skin pigmentation. Cybernetic implants would be either surgically attached to the body or grown internally by nanoprobes injected into the bloodstream. (TNG: "The Best of Both Worlds"; Star Trek: First Contact) The nature of these implants varied from drone to drone, depending on its intended function, but basic nodes of cordical, interlink & cortical array are implemented in every drone. In certain cases, parts of the body such as an eye or an arm would be amputated altogether to make room for the cybernetics. (VOY: "The Gift", "Dark Frontier") The implants of a fully assimilated drone allowed it to function for extended periods without shelter, food, water, or even air. A drone's only requirement would be a supply of energy to maintain the implants that in turn maintained its biological functions. This energy would be supplied during regeneration cycles within a Borg alcove. Upon receiving damage, drone would return to the cove for assessment of the damage. Severely damaged drones would be disassembled and scavenged for reusable parts. (TNG: "Q Who", "I Borg")

Borg drones were equipped with a myriad of technologies integrated into their bodies which enabled them to perform their duties within the Collective, several of which were universal to all drones. A neural transceiver kept them connected to the hive mind. (VOY: "Scorpion, Part II") A personal force field protected each drone from most energy-based attacks. (TNG: "Q Who") As of 2373, each drone possessed a pair of assimilation tubules embedded in one hand for the purpose of instantly injecting individuals with Borg nanoprobes. (Star Trek: First Contact) A cortical processor allowed a drone to rapidly assimilate visual information. Borg drones were also equipped with a neural processor, which kept a record of every instruction that particular Borg receives from the collective hive mind. Captain Picard used this processor to discover the Borg were attempting to use the Enterprise-E deflector dish as an Interplexing Beacon to contact the Borg in 2063. (Star Trek: First Contact)

Drones also contained failsafes designed to deactivate and even vaporize their own bodies, thereby allowing the Collective to eliminate damaged or dead drones without leaving remains to be exploited by outsiders. (TNG: "Q Who") The captured drone Third of Five also made comments indicating that this vaporization may have been a form of resource reabsorption. (TNG: "I Borg") One of these failsafes was intended to automatically deactivate drones experiencing strong emotional states, which the Borg interpreted as a sign of disconnection from the hive mind. (VOY: "Human Error")

History
The precise origins of the Borg are unclear. As of 1484 they were reported as controlling only a handful of systems in the Delta Quadrant, but by 2373 they had assimilated thousands of worlds. In addition to this stronghold in the Delta Quadrant, the Borg also dispatched vessels throughout the galaxy via transwarp conduits. (VOY: "Dragon's Teeth", "Scorpion", "Endgame")

A Borg vessel traveled back in time from 2373 in an unsuccessful attack on Earth in 2063. (Star Trek: First Contact) Drones which survived this defeat were discovered and reactivated by Human scientists in 2153, and transmitted a subspace message to Borg space before being destroyed by the Enterprise (NX-01). (ENT: "Regeneration") In 2293 the Federation offered aid to El Aurian refugees fleeing the Borg. (Star Trek Generations) However, each of these incidents contributed almost nothing to the Alpha Quadrant's awareness or understanding of the Borg Collective.

By the 2350s rumors of an alien race called "The Borg" had reached the Alpha Quadrant, inspiring exobiologists Magnus and Erin Hansen to set out in search of them. Their research took them all the way to the Delta Quadrant before their assimilation in 2356. (VOY: "The Gift", "The Raven", "Dark Frontier") Borg activity in the Alpha Quadrant went undetected until a series of unexplained attacks along the Romulan Neutral Zone in 2364. (TNG: "The Neutral Zone") The Collective's true nature was finally revealed to the Federation in 2365 when Q took the USS Enterprise-D to meet a Borg cube near the J-25 system. (TNG: "Q Who")

In late 2366 a Borg cube invaded Federation space and assimilated Jean-Luc Picard, whose tactical information contributed, along with the Borg's own vastly superior power, to Starfleet's disastrously one-sided battle with the cube, called the Battle of Wolf 359. A fleet of 40 starships assembled to combat the cube, and 39 of those ships were completely destroyed, with the cube emerging unscathed. The Enterprise-D recovered Picard and used his connection to the hive-mind to disable the cube before it could attack Earth. (TNG: "The Best of Both Worlds ", "The Best of Both Worlds, Part II")

During the 2370s, the Borg were beset by several major setbacks in the Delta Quadrant, all witnessed by the crew of the USS Voyager. The Borg-Species 8472 War decimated the Collective from 2373-2374. Voyager's liberation of Seven of Nine allowed Unimatrix Zero to create an active resistance movement in 2377. In 2378, a crippling blow was delivered to the Borg when Voyager discovered one of their transwarp hubs and destroyed it, killing the Borg Queen (again) and devastating the Unicomplex in the process. (VOY: "Scorpion", "Unimatrix Zero", "Endgame")