Grey

Grey aliens, sometimes known as Zeta Reticulans, Grays, or simply Greys, are by far the most commonly reported species involved in UFOlogical cases. Named for the coloration of their skin, these sapient humanoids have gathered fame and attention from researchers thanks to such infamous incidents as the Roswell UFO crash of 1947 and the Barney and Betty Hill abduction case in 1961; and their image has found its way into popular imagination and mass media to represent the archetypal, flying saucer-using, memory-erasing alien visitor who abducts subjects to study them.

Biology
In Fortean theories, the relationship between Greys and other races such as Reptoids is usually more complex, although it's frequently believed that the Greys themselves might be both reptilian and genetically-engineered in origin, and that they're employed; or in some sources explicitly enslaved; to act as a researching workforce and do the other race's bidding. Conversely, alternate ideas abound, including some picturing the Greys as benevolent, time-traveling descendants of Humans whose main purpose is to monitor and guide the development of their ancestors.

In the majority of UFO cases, the Greys have been consistently described as short, thin humanoids with grey and hairless skin and a conspicuously large cranium. Their eyes are large, black and almond-shaped, and their facial features are restricted to a pair of small slits in the place of the nose, and a small mouth. Their fingers are usually long and dexterous. Their bodies are proportionally small, and they don't appear to have genitals, which is noticeable due to the fact that they don't wear clothes. In some cases, they have been reported as capable of telepathy.

The body of Greys are more or less considered a vessel for higher dimensional beings to act in a lower density environment like the earth. An Is-Be in a Grey body can leave or invade this vessel according to their will much like an avatar. It is mostly designed to be a tool for example to steer spaceships, like an interface between an Is-Be and a machine. An Is-Be can control none, one or even more Grey vessels at the same moment. There are a couple of different alien races who use Grey bodies to focus energy in lower densities.

History
It is unknown when the Greys began their evolution but we do have an idea of where they're from, due to the fact that American whistle blower Bob Lazar was apparently working on a saucer from Zeta Reticuli 3, add that to the testimony of other whistle blowers about there being a Grey known as J-Rod on the premises, it is safe to assume that Zeta Reticuli 3 is their place of origin.

At an unknown point in time (most likely in humanity's early history) they mastered interstellar travel and managed to get to Earth.

The first notable encounter with the Greys was on July 8th 1947 in the town of Roswell, New Mexico, two crafts allegedly crashed in different places in the New Mexico desert, one crashed onto rancher's field and he even recovered some debris believing the craft to have been the property of the government, two bodies were recovered from the crashes and there was only one survivor, the survivor (Later called E.B.E (Extra-terrestrial Biological Entity) by the Americans) was interviewed by U.S officials where it was determined that the species was telepathic, telekinetic and came from the Zeta Reticuli Star System, E.B.E later died in 1952 due to disease.

Another notable encounter with the Greys was the Betty and Barney Hill Abduction, otherwise known as the Zeta Reticuli Incident, In 1961, Betty Hill and her husband Barney were driving along a New Hampshire road when they saw something in the sky that looked like a falling star, in actuality it was what appeared to be a large flying disk with two red lights on each side,when the craft began to fly away, the Hills persued the craft until the craft stopped, Barney got out of the car and looked at the craft with his binoculars, when he saw the creatures he was shocked, they tried to get away but they were soon abducted by the Greys, waking up later with no recollection of the last half hour, thy later under went hypnosis to recover the memories which revealed what had happened during the examinations, during the hypnosis, Betty drew a star map which she was shown on the ship, a member of Mensa later identified the primary stars shown as Zeta A and B Reticuli.

Popular culture

 * The species is featured in the 2007 movie Night Skies, based on an actual abduction case which took place during the Phoenix Lights event of 1997. The creatures portrayed on the film appear like skinny Greys with telepathic abilities and organic-based technology.
 * The species is featured in the Doctor Who animated special Dreamland, engaged in war with the Viperox. In the Third Doctor novel Devil Goblins from Neptune they are given the name Nedenah.
 * The Silents, although a different species, are similar to Greys in appearance and might be related.
 * There is a species called Grays in Alienology, that differ little from the standard definition of the species.
 * The Arilou Lalee'lay from Star Control are perpetually-mischievous that are intended to represent the Greys within that universe.
 * The Asgard from Stargate are typical Greys.
 * In the third episode of Extreme Dinosaurs three alien Greys appear imprisoned in a government facility, only to be freed by one of the Extreme Dinosaurs.
 * The aliens from the miniseries Taken are basic Greys.
 * Salarians in Mass Effect somewhat resemble the Greys.
 * In South Park a frequent Easter Egg in the show is the presence of what they call Visitors, aliens virtually identical to the mainstream idea of a Grey in every way.
 * The Furon are most likely inspired by the Greys.
 * The Greys also make an appearance in the 2001 MuckyFoot game, StarTopia, in which they can run the player's Sick Bay facilities.
 * The Interdimensional Beings from Indiana Jones and the Kingdom of the Crystal Skull are basic Greys.
 * The Colonists; a.k.a. Reticulans or Greys; are featured as part of the major mythology of The X-Files series.
 * The Babylon 5 universe features at least three species designed after the Greys of popular culture: the Streibs, the Zeners and the Vree.
 * The cartoon Buzz Lightyear of Star Command names them Roswellians and shows an inversion of the classic story; in which Buzz and his team crash land on the Grey's homeworld.
 * Roger from American Dad is an obvious example of a Grey in modern media.
 * Paul from the movie of the same name is a very deliberate example of a Grey.
 * The What from The Tick disguised themselves as a type of grey when they abducted the shows titular character.
 * The Sectoid from X-Com are that universe's variation of the concept.
 * Barash from Star Trek: The Next Generation belongs to a Grey-like species.
 * Greys appear (under the name "Grays") in the second and third Ratchet & Clank games.
 * In the 2013 horror-science fiction film Dark Skies, the main villains are named "the Greys".
 * The Vargon from the American Chillers novels are essentially Greys.
 * Men in Black features two species - Baltians and Arquillians - which bear some similarities to this species. However neither fits well in the size factor, the former being much taller than how the typical Grey is usually portrayed and the latter being several times smaller.
 * The mature form of the Skrit Na from Animorphs.
 * They are featured as one of the inhabitants of Area 51 in the animated comedy Escape from Planet Earth. 
 * The aliens from the 1977 science fiction film Close Encounters of the Third Kind are Greys.
 * The Duros from Star Wars are also physically Grey-like, despite being considerably taller than most other depictions.
 * Ankh-Venharis from the 1982 film Time Walker is revealed to be a Grey-like alien.
 * In the Dilbert animated cartoon series, a one-off gag has a pair of Greys arguing when one refers to itself as a "UFO", defending its position by insisting that it's a better name than their real one, Zyzphlahelmrn.
 * The Velgroxs from Transformers: Rescue Bots, appear to be a hideous Grey-like species.
 * Giygas from the Mother game series somewhat resembles a Grey in Mother 1.
 * The Sophons and Mavros from Endless Space are Greys with Spacesuits.
 * The Arcturans' appearance in Goosebumps 2: Haunted Halloween is based off the Greys.
 * In Transformers: Cyberverse, one of the heads on Starscream's Quintesson Judge body resembles a Grey.
 * In Samurai Jack, one large muscular Grey-like alien warrior.
 * The Abductors from Star Trek: Untold Voyages #5 are typical Greys.
 * In Final Space, the Lord Commander and Clarence both somewhat resemble Greys.
 * In Deus Ex Creatures called Grays are references to Greys.
 * In The Sims 2 series for PS 2, there is a household living in Pleasantview called Gray and both of the couples are aliens with a striking resemblance to the Greys.
 * In the Demon Accords series, they are known as the Vorsook.