The Borg are depicted as an amalgam of cybernetically enhanced humanoid drones of multiple species, organized as an inter-connected collective with a hive mind, inhabiting a vast region of space with many planets and ships. They operate towards one single-minded purpose: to add the biological and technological distinctiveness of other species to their own, in pursuit of perfection. This is achieved through forced assimilation, a process which transforms individuals and technology into Borg, enhancing individuals by adding synthetic components.
In their first introduction to the franchise, little information is forthcoming about the Borg or their origins and intents. In alien encounters, they exhibit no desire for negotiation or reason, only to assimilate. Exhibiting a rapid adaptability to any situation or threat, with encounters characterized by matter of fact 'resistance is futile'-type imperatives, the Borg develop into one of the greatest threats to Starfleet and the Federation. Originally perceived on screen as a homogeneous and anonymous entity, the concept of a Queen and central control is later introduced, while spokespersons for the Borg are sometimes employed to act as a go-between in more complicated plot lines.
In Star Trek, attempts to resist the Borg become one of the central themes, with many examples of successful resistance to the collective, both from existing or former drones, and assimilation targets, with at least one species being shown as having superior capabilities to the Borg. It is also demonstrated that it is possible to survive assimilation (most notably Jean Luc Picard), and that drones can escape the collective (most notably Seven of Nine), and become individuals, or exist collectively without forced assimilation of others.
The Borg were a concept born out of necessity for Star Trek to feature a new antagonist and regular enemy that was lacking during the first season of The Next Generation; the Klingons were allies and the Romulans mostly absent. The Ferengi were originally intended as the new enemy for the United Federation of Planets, but their comical, unintimidating appearance and devotion to capitalist accumulation or "free enterprise" failed to portray them as a convincing threat. They were subsequently reassigned the role of annoying but cute comic relief characters. The Borg, with their frightening appearance, immense power, and, most importantly, their sinister motive became the signature villains for the The Next Generation era of Star Trek.
Owing to their cybernetic enhancements, all Borg are far stronger than ordinary humans to varying degrees (depending on the species the drone came from). However, they never run to their destination, and hence most species can outpace them. Borg drones are resistant to phaser fire, being completely immune to the stun setting. In addition, all Borg drones possess personal shielding which collectively adapts to phaser fire. In various episodes, phasers tend to become ineffective after a dozen shots at most, depending on the settings and time between shots. Phaser frequencies can be altered to penetrate the shield, but the Borg adapt more quickly with each modulation.
Individual Borg rarely speak except in cases where such communication is necessary. Instead, they send a collective audio message to their targets stating that "resistance is futile", followed by a declaration that the target in question will be assimilated and its biological and technological distinctiveness will be added to their own. The exact phrasing varies among appearances, and the biological aspect is entirely absent when the Borg are first introduced.
When first introduced, the Borg are said to be more interested in assimilating technology than people, roaming the universe as single-minded marauders that have assimilated starships, planets, and entire societies in order to collect new technology. (TNG: "Q Who?") A Borg infant found aboard the first cube introduced suggested that they reproduced rather than assimilated lifeforms.
In their second appearance, "The Best of Both Worlds", they capture and assimilate Jean-Luc Picard into the collective by surgically altering him, creating Locutus of Borg. After this, lifeform assimilation becomes much more prominent in their overall behavior.
The method of assimilating individual lifeforms into the collective has been represented differently over time, only consistent in that infant and fetal humanoids have been grown in an accelerated state and surgically receive implants connected directly into the brain, as well as ocular devices, tool-enhanced limbs, armor, and other prosthetics. In Star Trek: First Contact, the method of adult assimilation is depicted with the more efficient injection of nanoprobes into the individual's bloodstream through a pair of tubules that spring forth from the drone's hand. Assimilation by nanoprobe is depicted on-screen as being a fast-acting process, with the victim's skin pigmentation turning grey with visible dark tracks forming within moments of contact where presumably blood vessels once existed. Within hours the victim is converted into a more or less complete drone. Because assimilation depends on nanoprobes, species with an extremely advanced immune system such as Species 8472 are able to reject assimilation.
Borg nanoprobes, each about the size of a human red blood cell (RBC), travel through the victim's bloodstream and latch on to individual cells. The nanoprobes rewrite the cellular DNA, altering the victim's biochemistry, and eventually form larger, more complicated structures and networks within the body such as electrical pathways, processing and data storage nodes, and ultimately prosthetic devices that spring forth from the skin. In "Mortal Coil", Seven of Nine states that the Borg assimilated the nanoprobe technology from "Species 149".
The capability of nanoprobes to absorb improved technologies they encounter into the Borg collective is demonstrated in the Voyager episode "Drone", where Seven of Nine's nanoprobes are fused with the Doctor's futuristic mobile emitter, creating a 29th century drone with capabilities far surpassing that of current drones. Fortunately for Voyager, this drone's enhanced capabilities are not disseminated throughout the collective; the drone, in fact, sacrificed itself to save Voyagers crew.
In William Shatner's novel The Return, Spock is nearly assimilated by the Borg, but is saved by the fact that he mind-melded with V'ger. This is because, according to Shatner's novel, the alien race that found V'ger was an earlier form of the Borg. Spock was saved from assimilation because he had part of the Borg Collective in his mind after he mind-melded with V'ger.
Star Trek: First Contact introduced the Borg Queen (played by Alice Krige). The Borg Queen is the focal point within the Borg collective consciousness and a unique drone within the collective, who originates from Species 125, that brings "order to chaos", referring to herself as "we" and "I" interchangeably.
In First Contact, the Borg Queen is seen as apparently present during Picard's former assimilation at the start as flashbacks in Picard's mind, and was believed destroyed along with that Borg cube years earlier. Here, she instead directs her attentions to Data. After his capture by her drones, she tries to tempt him with live flesh to comply with her. This Queen is destroyed when her organic components are melted off. She is destroyed in the Voyager episodes "Dark Frontier" and "Endgame", as well. In the Star Trek: The Experience attraction The Borg Invasion 4-D, the Borg Queen re-appears after Voyager returns to the Alpha Quadrant, but as Admiral Janeway attempts to kill her, she activates a transporter, allowing her to survive.
In the Star Trek: Voyager relaunch novels, the Borg Queen isn't a single, irreplaceable entity, but the product of a program called "The Royal Protocol" that shares its name with a Starfleet document outlining requirements when dealing with foreign royalty. This program is used to create a Borg Queen from any female Borg, commanding the technology within her to alter and adapt to the Protocol's specifications. In the relaunch novels, one of the leaders of Starfleet Intelligence gets her hands on "The Royal Protocol" and, with the use of an Emergency Medical Hologram, turns herself into a new kind of Borg Queen who cares about and loves her drones.
In the Mirror Universe story "The Worst of Both Worlds" by Greg Cox, the Queen is portrayed as a male. This version apparently can inhabit both male and female bodies, depending on the situation, but prefers females.
The Borg next appear in The Next Generations third-season finale and fourth-season premiere, "The Best of Both Worlds". In the third-season cliffhanger, Picard is abducted and subsequently assimilated by the Borg and transformed into Locutus, the Latin term for "he who has spoken". "Locutus" is the Borg method of describing the former Picard as the representative of the Borg in all future contacts related to humanity. Picard's knowledge of Starfleet is gained by the collective, and the single cube easily wipes out all resistance in its path, notably the entire Starfleet armada at Wolf 359, which consisted of 39 starships, some of which were sent from the Klingon Empire. The Enterprise crew manages to capture Locutus and gain information through him which allows them to destroy the cube. Picard is later "deassimilated".
In the fifth-season episode "I, Borg", the Enterprise crew rescues a solitary Borg who is given the name "Hugh" by Chief Engineer Geordi La Forge. The crew faces the moral decision of whether or not to use Hugh (who begins to develop a sense of independence as a result of a severed link to the collective consciousness of the Borg) as an apocalyptic means of delivering a devastating computer virus that would theoretically destroy the Borg, or to humanely allow him to return to the Borg with his individuality intact. They decide to return him without the virus. This is followed up in the sixth-season cliffhanger "Descent", which depicts a group of rogue Borg who had "assimilated" individuality through Hugh. These rogue Borg fell under the control of the psychopathic android Lore, the "older" brother of Data.
In cult leader-like fashion, Lore had manipulated them into following him by appealing to their restored emotions and exploiting their new-found senses of individuality and fear, hoping to turn them on the Federation. Lore also corrupts Data through the use of the emotion chip he had stolen from Noonien Soong (Data and Lore's creator). In the end, Data's ethical subroutines are restored (having been suppressed by Lore through use of the emotion chip) and he manages to deactivate Lore after a battle in which a renegade Borg faction led by Hugh attacks the main complex. Data reclaims the emotion chip, Lore is mentioned as needing to be dismantled (for safety) and the surviving Borg fall under the leadership of Hugh. The fate of these deassimilated Borg is not revealed.
After successfully driving Species 8472 back into their fluidic space, Seven of Nine attempts to assimilate Voyager and is severed from the hive mind, becoming a member of Voyagers crew. Seven of Nine's rediscovery of her humanity becomes a recurring plot point of the series. Flashbacks and allusions in several episodes, such as "The Raven", establish that prior to her assimilation, Seven of Nine was Annika Hansen, the child of scientists who studied the Borg in the Delta Quadrant independent of the Federation.
In "Drone", an advanced Borg drone is created when Seven of Nine's nanoprobes are fused with the Doctor's mobile emitter in a transporter accident. The drone, who adopts the moniker "One", involuntarily sends a signal to the collective, bringing a sphere to Voyager. One destroys the Borg ship and lets himself die to protect Voyager from further Borg pursuits.
In "Dark Frontier", Captain Kathryn Janeway decides to attack the Borg in the hopes of stealing a transwarp coil to aid in Voyagers journey home. The Borg Queen learns of the plot and offers Seven of Nine a deal to spare Voyager in exchange for her rejoining the collective. Voyager recovers the transwarp coil and uses it, with the Delta Flyer, to save Seven from the Queen. Voyager uses the transwarp coil to travel 20,000 light-years before it burns out.
In the Voyager finale, "Endgame", a version of Janeway from a future alternate timeline travels back in time to aid in Voyagers return to the Alpha Quadrant. This Janeway allows herself to be assimilated, delivering a neurolytic pathogen that disrupts the Borg to the point of killing the Borg Queen and destroying the Borg Unicomplex. Voyager uses a transwarp hub to travel back to the Alpha Quadrant.
Another Enterprise episode, planned for the fifth season of the show (which never materialized), would have featured Alice Krige as a Starfleet medical technician who encounters the Borg and is assimilated - thereby becoming the Borg Queen seen in First Contact.
In the Star Trek novel Probe, which takes place following the events of Star Trek IV: The Voyage Home, the Borg are mentioned obliquely in communication with the whale-probe as spacefaring "mites" (the whale-probe's term for humanoid races) who traveled in cubical and spherical spacefaring vessels; the Borg apparently attacked the whale-probe and damaged its memory in some fashion prior to the events of the film.
In the Star Trek Game Star Trek "Legacy" the Borg are featured mid way through the TOS era as "Assimilated Klingon ships" then in the final mission once the player has completed the primary objective a confrontation with T'urell ensures where she will depart and the player must destroy a Borg Sphere.
The Peter David novel Vendetta reveals that the planet killer weapon from the Original Series episode "The Doomsday Machine" is a prototype for a weapon against the Borg. David revisited this concept in a 2007 sequel novel, Before Dishonor.
The origin of the Borg is never made clear, though they are portrayed as having existed for thousands of centuries (as attested by Guinan and the Borg Queen). In Star Trek: First Contact, the Borg Queen merely states that the Borg were once much like humanity, "flawed and weak," but gradually developed into a partially synthetic species in an ongoing attempt to evolve and perfect themselves.
In TNG's "Q Who.", Guinan mentions that the Borg are "made up of organic and artificial life [...] which has been developing for [...] thousands of centuries." In the later episode of Star Trek: Voyager, "Dragon's Teeth", Gedrin says that before he and his people were put into suspended animation over 900 years earlier, the Borg were just a few assimilated colonies inside the Delta quadrant and viewed somewhat like a minor pain. Now awake in the 24th century, he's amazed to see that the Borg control a vast area of the Delta quadrant.
The Star Trek Encyclopedia speculates that there could be a connection between the Borg and V'ger, the vessel encountered in Star Trek: The Motion Picture; this is advanced in William Shatner's novel, The Return. Coincidently, in the novelization of Star Trek: The Motion Picture (written by Gene Roddenberry), the V'ger entity notes that the Ilia probe is resisting the programming given to it because of residual memories and feelings for Decker. When V'ger becomes aware of this, it is aware that "the resistance was futile, of course".
The extra section of the game Star Trek: Legacy contains the "Origin of the Borg", which tells the story of V'ger being sucked into a black hole. V'ger was found by a race of living machines which gave it a form suitable to fulfilling its simplistic programming. Unable to determine who its creator could be, the probe declared all carbon-based life an infestation of the creator's universe, leading to assimilation. From this, the Borg were created, as extensions of V'ger's purpose. Drones were made from those assimilated and merged into a collective consciousness. The Borg Queen was created out of the necessity for a single unifying voice. However, with thoughts and desires of her own, she was no longer bound to serve V'ger. This explanation, however, is not canon.
In the graphic novel Star Trek: The Manga, the Borg resulted from an experiment in medical nanotechnology gone wrong. An alien species under threat of extinction by an incurable disease created a repository satellite containing test subjects infused with body parts, organs, and DNA of multiple species along with cybernetic enhancements put in place by advanced medical technology. The satellite was maintained by nanomachines. The medical facility deteriorates and so too does the programming of the nanomachines. The nanomachines began infusing themselves into the patients, interpreting them as part of the satellite in needing repair. Among the patients is the daughter of head medical researcher of the satellite. The satellite eventually falls apart in an encounter with an away team from the Enterprise under the command of James T. Kirk. In the final moments of the satellite's destruction and the escape of the crew members of the Enterprise with the patients, the subjects display qualities inherently resembling the Borg; injection of nanoprobes, rapid adaptation to weaponry, and a hive mind consciousness, as all the subjects begin following the whim of the daughter. As succumbing to the disease was inevitable, and the corrupt nanomachine programing infused itself into the bodies, the final image of the page of the manga Borg origin is left with the daughter turned Borg Queen, stating, "Resistance is futile."
Activision at one point planned to release Star Trek: Borg Assimilator, in which the player would play a Borg, but later canceled the game.