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Is the Mad Hatter a rabbit in Alice in Wonderland?
It is unclear as to whether or not the Mad Hatter from Alice in Wonderland was designed as a character to represent any metaphorical idea. However, it is well regarded that the character was based on...
There is no evidence in Lewis Carroll's books to suggest that the Hatter is an alien, so the answer is no. (Of course, maybe the Hatter knows something that Lewis Carroll doesn't) ;)