Stranger in a Strange Land by Robert Heinlein (1962) – A Human is left on mars for The Reds Abbey Road signatures shirt and then brought back home, but is now more alien than human. Extremely popular at the time, with the word Grok even entering common parlance. The book is slow to start off with and bits of it are quite silly in retrospect, other bits either sexist or feminist depending on your viewpoint. There is definitely something there though. Certainly not a flawless work, in fact it is very much more flawed than many of the books ranked lower on this list, but there is something that sticks with you about it. It is massively referenced in pop-culture and just feels important as a novel even if bits will make you cringe.
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