Extraterrestrials in fiction

An extraterrestrial or alien is a lifeform that did not originate on Earth. The word extraterrestrial means "outside Earth". Extraterrestrials are a common theme in modern science-fiction, and also appeared in much earlier works such as the second-century parody True History  by Lucian of Samosata.

History
The 2nd century writer of satires, Lucian, in his True History claims to have visited the Moon when his ship was sent up by a fountain, which was peopled and at war with the people of the Sun over colonisation of the Morning Star.

Antiquity
The way people have thought about extraterrestrials is tied to the development of actual sciences. One of the first steps in the history of astronomy was to realize that the objects seen in the night sky were not gods or lights, but physical objects like Earth. This notion was followed by the one that celestial objects should be inhabited as well. However, when people thought about such extraterrestrials, they thought of them simply as people, indistinguishable from humans. As people had never considered a scientific explanation for the origin of mankind or its relation with other lifeforms, any hypothetical rational lifeforms had by necessity to be humans. Even in mythology, all deities are mostly humanlike. For example, Voltaire's Micromégas features people from Saturn, who are simply of higher proportions.

This was changed by the 1859 book On the Origin of Species by Charles Darwin, which proposed the theory of evolution. This book caused a revolution in fiction as much as it did in science, as authors began to imagine extraterrestrial races completely different from human beings. With the rationale that evolution in other worlds may take completely different directions than on Earth, aliens began to be described as creepy monsters. Usually, authors used features from other animals, such as insects, crabs, and octopuses. Some such aliens are the octopean Martians from The War of the Worlds (1898), the Selenites from First men in the Moon (1901), the birdlike Tweel from A Martian Odyssey (1934) and even a sentient star in Star Maker (1937).

Modern times
The Barney and Betty Hill incident took place in 1961 when the couple claimed that they were abducted by aliens and subjected to invasive experiments. It was the first recorded claim of an alien abduction, soon followed by others. The description of the aliens made by the Hills, with oversized heads, big eyes, pale grey skin, and small noses captivated the public imagination and was later used by TV shows and films. This started the grey alien archetype. According to Wade Roush, a science and technology writer, "The standard depiction of aliens at that point became the little grey man. So, when Steven Spielberg came along and made probably what are the two most influential movies about aliens – Close Encounters of the Third Kind, and ET the Extra-Terrestrial – the aliens and those movies were both basically variations on the 1950s and 1960s little green or little grey man image".

The advent of TV and films, with extraterrestrials played by actors, toned down the fantasy. For budget reasons, humanlike aliens with just some specific non-human body features became the new standard. This is especially noticeable in the Star Trek franchise. This changed again since the 1990s with the advent of computer-generated imagery (CGI), and later on as CGI became more effective and less expensive, as it allows to generate bizarre lifeforms without being constrained to actors with costumes or mechanical effects.