Comic Code Authority

Most people think of censorship as being done by outside forces. However, the Comic Code Authority was created by the comic book companies themselves.  In 1954, a book called Seduction of the Innocent blamed comic books for Juvenile Delinquency. Soon, the public turned against comic books. So the comic publishers formed the Comic Code of Authority. However, the code basically destroyed horror comics temporarily. Here were the rules in a nut shell:

• No Vampires, werewolves, ghouls and zombies
• Excessive violence was banned.
• No nudity at all
• "Horror" and "Terror" couldn't be in a comic title, "Crime" could be used to an extremely limited extent.
• No sexual art
• No liquor, tobacco, knives, fireworks or products of "questionable nature" ads
• No drugs at all

If they followed the code, the cover would of the Comic Code Authority "stamp" (seen here). Despite these rules, they approved a comic featuring the most racist comic book character in history: Egg Fu (he is a racist amalgam of every offensive Asian stereotype and egg fu). However despite the fact most comics followed the code some did not, most notably the Underground Comix (which had nothing to do with the naming of this site) and Mad (due to it's magazine format). In 1971, Stan Lee wrote an anti-drug Spider-Man story, but the code disapproved of it, so he did without the code. This lead to minor revisions to the comic code most notably the unbanning of vampires, werewolves, ghouls, but not zombies. So, they were referred to as "zuvembies". By the 21st century, the comic code dropped in power and Archie and DC comics became the only major comic companies to use the code.
References:
http://en.wikipedia.org/wiki/Comics_Code_Authority
http://upload.wikimedia.org/wikipedia/en/d/df/CCA.gif
http://upload.wikimedia.org/wikipedia/en/c/cb/Wwoman158.jpg
http://www.comicvine.com/egg-fu/29-24028/