Gray

Grays are genetically-engineered creatures appearing in Deus Ex and Deus Ex: Invisible War.

Origins
Grays were the products of experiments undertaken by Majestic 12 at Area 51. These experiments were collectively known as the "bovine manipulation project," which was underway by 2028 or earlier. Grays were created by crossing the DNA of different creatures, including bovines (cattle). Hence, grays, along with other genetically-engineered creatures such as the greasel and the karkian, are known as transgenics.

Grays have a silvery-gray complexion and are hairless. They also have enlarged heads, dark eyes, and long, gangling arms and legs. Grays have the ability to "spontaneously generate radiation as a form of attack," and are highly resistant to a number of harsh environment conditions. Grays thrive in frigid or radioactive environments, but they are also capable of living in warm and non-radioactive environments.

Their appearance closely resembles the popular depiction of aliens, resulting in speculation that grays were produced from cells of aliens that crashed at Roswell. In actuality, grays are fully engineered transgenics, and are not aliens. Nonetheless, their alien-like appearance was exploited by the Illuminati and Majestic 12 as a propaganda tactic in diverting attention away from actual research at Area 51. One Area 51 worker speculates that grays are monkeys genetically engineered not to have hair. However, the involvement of monkeys in the creation of grays has not been specifically confirmed.

When the bovine manipulation project was first undertaken, the gray lifeform was viewed as a failure. However, DeBeers suggested to Bob Page the idea of using them to protect MJ12 facilities and taking advantage of their physical appearance as a tool for misdirection. By 2051, grays were being used to guard top secret MJ12 facilities, including Area 51. Using their known genetic profiles, grays were also produced molecule by molecule by the universal constructor in Area 51.

Post-Collapse
Following the destruction of Area 51, which resulted in the collapse, JC Denton took care of the grays in Antarctica. In return, the grays helped maintain JC's sanctuary while JC went into stasis. Thus, the grays became a key ally of ApostleCorp. The grays in Antarctica were originally brought there by VersaLife to test their reactions to extreme conditions. They were created to be a new generation of hardy troops, but were also made to be sterile as a safeguard measure. Some were engineered for combat, while others were engineered to be leaders.

In 2071, the grays in Antarctica are attacked by the Templars, who are opposed to ApostleCorp.

Deus Ex
In Deus Ex, grays are part of the Animal class of scripted entities. They are always hostile to the player whenever encountered. Grays have full immunity to multiple damage types: Stunned (riot prod), TearGas (pepper gun and gas grenade), HalonGas (fire extinguisher), PoisonGas (from poisonous barrels and other environment features), Radiation, Flamed (flamethrower), and Burned (plasma-based weapons). However, they are fully susceptible to Tranquilizer Darts, which will kill them outright because Animal-class entities cannot be rendered unconscious, and which allow the player to take them out from a distance without entering the radioactive aura. A single tranquilizer dart, with the pistol skill at "trained" or higher, is enough to take out a Gray. When shot, the creature will still give chase to the player but get constantly stunned as the drug takes effect until it finally dies.

Grays have three attacks:
 * A swipe attack (WeaponGraySwipe).
 * A ranged attack (WeaponGraySpit) that inflicts radiation damage.
 * An aura-type effect that inflicts continuous radiation damage to the player, with a base damage of 10, if the player is within a distance of 256 units (16 feet) from the gray. The aura-type effect is a hard-coded effect and is not implemented in the form of a weapon. It also damages only the player, and does not damage any non-player characters or other objects in the game environment.

Despite being somewhat humanoid in appearance, damage multipliers that apply to human NPCs do not apply to grays. Therefore, the headshot multiplier (8x damage) available against human NPCs is not available against grays.

Deus Ex: Invisible War
In Deus Ex: Invisible War, grays are able to communicate with Alex Denton, and are also very friendly to any ally of ApostleCorp. The intelligence of the grays in Invisible War is explained by their leader in Antarctica, who reveals that some grays were engineered for tasks like combat, while some grays were engineered to be leaders. The gray leader will also explain their origins to Alex:

Due to their lack of biomod infusions, grays cannot go through the portal, and so must be transported the long way to the ApostleCorp facility in Trier.

Grays will readily attack any enemy of ApostleCorp, including the player (Alex Denton), if he or she is affiliated with another faction in the endgame. Because grays are genetically-engineered, the Knights Templar attempt to kill them whenever possible. In the Templar ending, a gray can be seen hanging from a noose.

Trivia

 * According to developer commentary in the Deus Ex Bible, the fact that Grays aren't actually aliens was intended to be a twist to alien cover ups. The commentary states: "the aliens weren't being covered up, they were the cover-up. The idea of the aliens being the method used to distract people from the truth is a very good one. The idea that those aliens are not really aliens but instead a total fabrication is fun."
 * As to how grays were originally made, commentary in the Deus Ex Bible states: "perhaps the cows were used as incubators and the grays either burst out, unlikely, or were surgically removed."
 * Design document v. 13.12 states that Grays were created from "the genetic material of abducted humans and mutilated cattle," suggesting that grays are also based on human DNA. However, basis in human DNA is not canonically mentioned in either the Deus Ex Bible or any title in the series.
 * In the official strategy guide for Deus Ex, the gray's attack is named "psionic blast." In the corresponding strategy guide for Invisible War, the attack is simply named "radiation attack."