The Greys reference article from the English Wikipedia on 24-Apr-2004
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Greys

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Greys are a type of intelligent extraterrestrial life that appear commonly in modern conspiracy theories, particularly UFO conspiracy theories and other UFO-related paranormal phenomena. They also appear in some science fiction.

Greys are generally described as short, slender humanoids with hairless grey skin (hence the name) and large heads with enormous black eyes and small mouths. It is interesting to note that this description resembles a neotenous human, ie, a human with infant-like features. Greys made their first significant appearance in the 1977 film Close Encounters of the Third Kind.