In an odd case, TSR told R.A. Salvatore to bring back Wulfgar, or they would do have someone else do it for them. What makes it odd is that Drizzt was clearly the breakout hit character, with Wulfgar as a mostly unneeded sidekick. Salvatore did the best he could, though, and in the end got some good stories out of it and wrote the character out again (this time much as he had written out the barbarian tribes the character belonged to shortly after the character's "death").
In another case, Salvatore was told that he would have to kill off Artemis Entreri, as the game was eliminating the assassin class and all assassins in the setting were going to be killed off as part of a ritual to empower the dark god Bane. Salvatore, not wanting to lose a good character, countered that Entreri wasn't an "assassin", but a fighter/thief who killed people for money. TSR backed off. (Later, Wizards brought back assassins as a prestige class for 3rd Edition. Entreri had one level in it.)
The Goldfish Pool and Other Stories, a short story by Neil Gaiman is not an example, but it is about Executive meddling, plus truly epic amounts of Adaptation Decay. A writer is called in to Hollywood to work on a film adaptation of his hit novel, Sons of Man, which is a speculative story about Charles Manson being possessed by a demon, and the children he sired of the women in the Manson family coming under the power of that demon, with a sole daughter he had trying to stop them. By the time the ever-changing Hollywood executives are done with it, it's a slasher plot called When we were Badd about a serial killer named Jack Badd who posessed a video game after execution and possessed the kids who played it, with the now-male protagonist saving the day by burning the electric chair the killer was executed in.
It ends with the writer's offhand quote of a song lyric being taken out of context and used as the plot for a completely different movie about a woman trapped in a loveless marriage. At that point he gives up and goes home.
Gaiman has a long history of Hollywood stresses; in addition to the aforementioned Jon Peters run at Sandman (resulting in what Neil described as "the worst script I've ever read"), he was approached on an adaptation of Anansi Boys. Y'know, the book where the main characters are the children of African deity Anansi, and thus they (and a lot of their acquaintances) are black. The first question asked was apparently, "Is there any way we can make them white?"
Writers in the Star Wars Expanded Universe have editors going over work and vetoing what they don't think fits into canon. Some of them...aren't all that bright. Timothy Zahn, in a panel summarized here, complains about editors claiming that R-2 can't fly Luke's X-Wing in Specter of the Past.
"So," Zahn said, with absolutely the driest expression and tone of voice you ever saw, "I pointed out that way back in Heir to the Empire, Artoo flew the X-wing to Coruscant on his own. 'But Artoo can't fly the X-wing.' Okay, in ESB, one of your own movies, Luke's X-wing was inside the Hoth base, but Luke meets it outside. 'But Artoo can't fly the X-wing.' Then later in the movie, Luke tells Artoo, "No thanks, I'll keep it on manual for a while." Manual indicates that there must be an automatic. 'But Artoo can't fly the X-wing.'"
"Finally," he said, "I figured out what it was that bothered them. It wasn't Artoo flying the X-wing; it was his docking the ship with the Starry Ice without the aid of tractors." He added exactly three words to the existing scene, with Faughn now telling Luke that the Starry Ice had a pair of half-ports "with tractor assists". The editors were happy, and all was well.
One that did work out was that Lucasfilm shot down Timothy Zahn's original name for the Noghri which was Sith, to explain why Darth Vader was known as the Lord of the Sith. The reason, of course, was that Zahn didn't realize that George Lucas already had something very different in mind for the meaning of that title.
Later events made fans theorize that George Lucas realized that he had virtually identical stories for Anakin Skywalker and Anakin Solo (hope of the Jedi Order, deep connection with the Force, skill with technology, and oh yeah, a fall to the Dark Side that plunges the Galaxy into war, destroying a republic). So in the end, they killed off Anakin Solo and gave his fall to the Dark Side plot to older brother Jacen.
Legendarily, Robert A. Heinlein's Stranger in a Strange Land was pared for both size and content to meet publisher demands. Thankfully, the editing was done meticulously by Heinlein himself, so the novel came out more or less as intended. Following his death, the unedited version was released by Heinlein's widow. Your Mileage May Vary on which version is better.
Lindsey Davis' Falco novels suffered similar fates of Americanisation, or would have, had she not been adamant. See here for her very funny article about it all. Read "A Gentle Corny Rant" on this page.
The British publisher did their own meddling on the first book. They were the ones who insisted the author go by J. K. Rowling since it was felt boys wouldn't want to read a book written by a woman. They also wanted to cut the troll scene where Harry and Ron save Hermione.
Terry Goodkind's book Wizard's First Rule had at least one instance of the use of the titular rule scratched out by the editor. Maybe it was for the better, since we all know where it went from there...
The final book in the third Warrior Cats series had its name changed from Cruel Season to Sunrise because HarperCollins felt the original title was too sad and not appropriate for the younger readers. Not only does this cause a lot of confusion with the final book of the second series (Sunset), but changing the title still doesn't change the fact that the book is sad. To make things even more mindboggling, the authors were allowed to use the phrase "cruel season" in the blurb of the very next book.
Umberto Eco once wrote a humorous piece, "Editorial Revision", about (fictitious) editorial changes for the better in famous literary works; for example, "The Waste Land" by T. S. Eliot originally started like this (not exact quote): "April is the cruellest month. But March isn't very good either".
In a minor example, Jim Butcher originally wanted to call the first book of The Dresden FilesSemiautomagic. For whatever reason, the editor or publisher didn't like it, and so he called it Storm Front instead, creating the trend of two word titles with each word having the same number of letters.
A positive example: Isaac Asimov wrote a story in which energy beings come to Earth and purchase Jupiter from humanity to use as an advertising billboard for their passing ships. Asimov titled the story "It Pays", but an editor, without consulting Asimov, changed it to "Buy Jupiter". Asimov, being the punster that he was, liked it so much he used it as the title for the paperback collection which contained the story.
Another Asimov example features his most famous work, I, Robot. The first story, "Robbie", was originally titled "Strange Playfellow", but was changed, and the collection itself had a different name until Asimov was convinced to make it I, Robot (there was already another work by another author with the same name, and he felt bad about taking the name, but his publisher convinced him otherwise).
Jules Verne initially made Captain Nemo a Polish aristocrat who was fighting Russians after his family was killed by Russian soldiers during the ill-fated January Uprising. His editor, Pierre-Jules Hetzel feared that this might cause diplomatic problems because Russia was allied with France at the time. With Franco-Prussian War looming on the horizon Verne was persuaded to make Nemo a mysterious stranger fighting the British and later (in The Mysterious Island) he made him an Indian Prince while retaining motivation (family lost during the brutal quelling of Indian Uprising).
The German publisher "Aufbau Verlag" loves meddling with their translations of classics. Most glaring example is Victor Hugo'sLes Misérables - from somewhat about 1400 pages (in original length of the German translation) they left about 900. They cut out Valjean's theft on Petit Gervais, several of his My God, What Have I Done? moments, a good chunk of Marius' backstory, the characterization of several important minor characters... and also quite a few of Hugo's Author Tracts.
The Twilight Saga was originally supposed to be two books long, going straight from Twilight to Breaking Dawn. (Then called Forever Dawn.) It was Stephenie Meyer's editor who suggested that Bella's senior year be drawn out, resulting in New Moon and Eclipse. (It was also suggested that Forever Dawn was "inappropriate" for young adult audiences, though.)
The Jungle was subjected to this by Doubleday. The original edition published by the socialist newspaper Appeal to Reason was singularly focused on the hell the main characters, an immigrant family, go through because they are poor, are not fluent in English, and because the businessmen run everything and was obviously meant to make readers see the horrors of wage slavery. Doubleday, however, was a corporation, and it therefore didn't take too kindly to The Jungle's criticism of corporations and the ways in which they exploited their workers. They forced him to make the family less ethnic, amend some passages so that their lives were not so unfair, and make the passages about the tainted food more graphic. Most people read Doubleday's edition and they were singularly focused on the unsanitary conditions of the factories making food products and the book is now taught as an exposure of the corruption that led to tainted food. The only hint that American history textbooks will give as to the disparity between Sinclair's intentions and the public's response is his quote "I aimed at the public's heart and by accident hit its stomach."
In probably one of the most heinous examples, L.J. Smith was fired from writing her own series. The article speculates that this was because they didn't like the romantic pairing she was planning on going with in the ending, but as far as I'm aware, no reason has been officially given. Shipping: Serious Business.
