Reptoids are a humanoid reptilian species who are either supposed alien threat that is discussed in the UFO culture as well as some conspiracy movements or play prominent roles in various fantasy folklores.
In Sci-Fi Theory
They are said to work in alliance with the Greys as either equals or as the masters (in some versions they aren't allies at all) - in almost all stories involving them the Reptoids are portrayed as malevolent in regards to humanity and don't seem to shy from their plans to enslave or replace humanity. The idea of reptilians was popularised by David Icke, a conspiracy theorist who claims shape-shifting reptilian aliens control Earth by taking on human form and gaining political power to manipulate human societies. Icke has claimed on multiple occasions that many of the world leaders are, or are possessed by, so-called reptilians.
If the accounts of some UFO abductees are to be believed Reptoids are not just in conflict with humanity but are also a major threat to all mammalian life in the galaxy (save for the Greys) - why Reptoids have such an intense hatred for mamalian life is not explained, though it could simply be down to arrogance or xenophobia.
Non Sci-Fi Tale
Some people believe the Reptoids are part of an ancient race that lived on Earth prior to current humanity and seek to reclaim their world while others think they are completely foreign beings that have somehow found Earth and seek it as their own - very few believe the Reptoids to be benevolent and even amongst other supposed otherworldly species Reptoids are often portrayed as dangerous.
According to the more radical groups of conspiracy theorists Reptoids have also managed to infiltrate humanity and are ruling the world in the form of powerful political leaders, capable of taking human shape at will and slowly working on the completion of the fabled New World Order or Illuminati.
Some radical Christain groups deny Reptoids are aliens at all but believe they are part of a Demonic Conspiracy.
Outwith the fantastical stories of New Age groups, UFO lore and conspiracy theorists the Reptoids have enjoyed more mainstream success as standard alien/monster-type in fiction.
See Gorn (Star Trek).
See The Visitors.
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