The Greys or Grays are a category of humanoid extraterrestrial beings named for their characteristic grey skin. They are thought by some researchers to be a caste of human-extraterrestrial hybrids, rather than a distinct race. Greys are ubiquitous in abduction literature and represent the typical image of an alien being in popular culture, in large part due to the wide reception of Whitley Strieber's 1987 book Communion and the 1989 film of the same name.
Physical descriptions of Grey beings differ widely, but in all cases share the distinctive characteristics of a humanoid with pale or grey-colored skin, very large eyes that are predominantly or completely black in color, a very slim and hairless body, a large head in proportion to the body (usually with a sharply pointed chin), and below-average height in comparison to humans. Other commonly reported features include a small, slit-like mouth and a nose that is either very reduced or absent with the exception of the nostrils. In some cases a mouth and nostrils are not reported at all (as in the 1976 Allagash, United States abductions), while in other cases features such as an iris and cranial hair are reported in addition to these (as in the 1994 Ruwa, Zimbabwe landing). True Greys lack any indication of having genitals, unlike Hybrids.
"They were ugly and small with slightly larger heads and no hair. They had huge black eyes and neither ears nor noses, only holes. They had grey skin, flat faces, and their hands were covered with small bumps." - Carlos Manuel Mercado in interview with Jorge Martin, 1988 
According to David Jacobs
Grey beings come in two basic forms: small greys (0.9 – 1.1 meters, or 3 – 3.5 feet) and tall greys (1.2 – 1.4 meters, or 4 – 5 feet). There are no obvious physical differences between the two forms aside from height. The skin color is grey with a texture that appears relatively smooth (but is rough to the touch). The eyes are large, totally black and distinctly almond-shaped with a downward slant. There are two nostrils in the center of the face with an external nose that is either absent, or present but very reduced. There are earholes on either side of the head with no external ear or pinna. The mouth is a small, narrow horizontal opening. The forearms are long by human standards of proportion and the limbs are thin.
David Jacobs theorizes that Greys represent a hybrid workforce created using genetic material from humans and at least one extraterrestrial race, possibly the Mantoids. This is based on their human-like anatomy as well as their observed role in the abduction program, and is supported by evidence that Grays display division of labor by body size and subordination to other extraterrestrial types. Small Greys perform repetitive tasks such as abducting humans, escorting humans while they are onboard the spacecraft, dressing and undressing humans, and returning humans to their normal environment, as well as the associated mental procedures of blocking abduction-related memories and planting screen memories. They also perform more menial functions aboard the spacecraft, such as cleaning up human bodily fluids. Tall Grays perform complex medical procedures such as the extraction of gametes and implantation of fetuses, and may be assisted in these procedures by small Grays. Tall Grays also engage abductees in "staring procedures", in which the Gray makes direct eye contact with the abductee at a distance of no more than a few inches or centimeters. The abductee is typically immobilized during this process. The experience of abductees during these staring procedures indicates that they are a means of imparting or extracting information to and from the human mind and inducing a range emotions including sexual excitement in male and female abductees. By some accounts, Grays are able to induce orgasms in women through a staring procedure in order to stimulate immediate ovulation, following a medical procedure in which the woman's normal ovulation process is modified by unknown means. Staring procedures are also used by Hybrids and Insectoids.
Communication by Grays is entirely telepathic, with humans experiencing communication as words, images and feelings that are perceived mentally. Grays appear to feed primarily feed by immersion in what is presumably a fluid formula, whereby nutrients are absorbed through the skin. The mouth, therefore, is non-functional. Furthermore, Grays are not typically reported as breathing either via the mouth or the nostrils. The chest does not rise and fall to indicate inhalation and exhalation, nor are abductees in close physical proximity to Grays able to feel the breath of the being. This may indicate that respiration in Grays, like nutrition, occurs through the skin rather than via an orifice.
- Carlos Mercado quoted in "Grey Aliens Took Man From Puerto Rico To Their Underground Base In 1988 And Told Him They Want Peace"
- David Jacobs, 2015, "Walking Among Us", Disinformation Books, San Francisco
- David Jacobs, 1999, "The Threat", Simon & Schuster, New York City - https://www.bibliotecapleyades.net/vida_alien/thethread/thethread.htm#Contents