Watchmen is the only comic to be included in Time Magazine's 100 best English-language novels from 1923 to present, even topping it at one time. It's widely considered to be the greatest comic ever by millions of sweaty comic fans, about half of which have actually read it. It's also said that the complex and mature nature of the story changed comics forever, and many commend DC Comics for having the balls to publish it in the first place.
The Simpsons have done an episode about every entry on this list, by the way
But it Only Exists Because...
DC Comics didn't have the balls to publish it... not with the original characters anyway. In the 80s, DC bought the rights to an entire set of superhero characters from Charlton Comics. DC was looking for something to do with their new properties, so rising star Alan Moore put together a proposal based on those characters and submitted it to his bosses. To their credit, DC approved the idea. However, they also realized the characters would be rendered useless by the end of the comic (by virtue of being dead, intergalactic nudists or chubby, lovable losers too busy bangin' chicks way out of their league to fight crime). Not willing to lose the guys they had just bought after a single story-arc, they asked Moore to change all the names and tweak the appearances. Bringing his typical respect for authority to the task, Moore put as little effort as possible into disguising the source material. So for example, the guy with the blue suit, the goggles and the ship...
Became the guy with the brown suit, the goggles and the ship:
And the guy with the fedora and no face...
Became the guy with the... fedora and no face:
One can forgive Moore for phoning it in a little; the man was nurturing a decade-spanning hobo beard and a cutting hatred for capitalism; he had other shit on his mind.
F.W. Murnau's classic 1922 film Nosferatu established several vampire tropes: Chief amongst them being the whole "they sleep by day and can be killed by sunlight" thing, which was so rudely bedazzled by some modern interpretations. Nosferatu was the first significant vampire film (predating Universal's Dracula by a decade) and we have it to thank for one of the most influential movie monsters in history.
But it Only Exists Because...
When Bram Stoker's estate denied Germany's Prana Film the rights to Dracula, they didn't even have the decency to turn the characters into plumbers and apes--which would have stepped all over our new screenplay Donkey Kong (But They're All Vampires): A Love Story. No, they just changed all the names, which, given that this was a silent film, only really required whatever the 1922 equivalent of "CTRL+F, Replace" was (we have to assume it involved pelting an intern with the heaviest object within reach, even back then).
So, Count Dracula became Count Orlok, Jonathan Harker became Thomas Hutter, and his wife Mina, in a Matt Groening-esque display of creativity, became Nina. They couldn't use the word "vampire" technically, so they flipped over a couple of pages and stole the term "nosferatu" from a less famous part of Stoker's novel.
Well at least they came up with the whole death by sunlight thing. Although, in the context of the "give a man a fish / teach a man to fish" parable, that might be the laziest contribution on this list.
Ray-Ban ads and death by sparkling: Thanks Nosferatu!