Borg

"We are the Borg. Lower your shields and surrender your ships. We will add your biological and technological distinctiveness to our own. Your culture will adapt to service us. Resistance is futile."

- The Borg

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

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

Upon assimilation, a drone will cease to grow body hair and develop an ashen, grayish skin coloration, ignoring original skin pigmentation. Cybernetic implants will 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 varies 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 will be amputated altogether to make room for the cybernetics. (VOY: "The Gift", "Dark Frontier") The implants of a fully assimilated drone allow it to function for extended periods without shelter, food, water, or even air. A drone's only requirement will be a supply of energy to maintain the implants that in turn maintain its biological functions. This energy is supplied during regeneration cycles within a Borg alcove. Upon receiving damage, a drone will return to the cove for assessment of the damage. Severely damaged drones will be disassembled and scavenged for reusable parts. (TNG: "Q Who", "I Borg")

Borg drones are equipped with a myriad of technologies integrated into their bodies which enable them to perform their duties within the Collective, several of which are universal to all drones. A neural transceiver keeps them connected to the hive mind. (VOY: "Scorpion, Part II") A personal force field protects each drone from most energy-based attacks. (TNG: "Q Who") As of 2373, each drone possesses 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 allows a drone to rapidly assimilate visual information. Borg drones are also equipped with a neural processor, which keeps 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 contain 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 is intended to automatically deactivate drones experiencing strong emotional states, which the Borg interpret as a sign of disconnection from the hive mind. (VOY: "Human Error")

Although a person assimilated into the borg becomes a drone, it is possible for a drone to gain a sense of individuality if they are separated from the Borg queen for a long enough period of time. The most notable case of this are Seven of Nine and Jean-Luc Picard. A particularly interesting case was Hugh, who not only developed a sense of individuality but also managed to spread it among other borg drones.

Enterprise
In Star Trek: Enterprise, there were two drones found in the Arctic (probably survivors from First Contact)

The Next Generation
The second encounter with the borg was made by Captain Jean-Luc Picard of the U.S.S. Enterprise when he was visited by Q, who decided to introduce him to the true unknown dangers of the galaxy. He used his powers to move the Enterprise into an uncharted region of space, where the crew of the Enterprise confronted a Borg Cube.

Voyager
In Star Trek: Voyager, the crew came in to contact with the Borg many times. On one occasion, there was a transporter accident which merged 7of 9's nanoprobes with the Doctor's mobile emitter and some D.N.A from a crewman, which created a Borg drone with the technological level of the 29th century. However, it allowed itself to be killed.