I notice that everyone here appears to associate the author's views with being something negative, which doesn't always have to be the case imo. Plenty of authors have strong opinions and convictions that shine through in their work without necessarily degrading the quality or feeling forced in any way.

Well the most obvious example I think would be Atlas Shrugged, the novel written by Ayn Rand in 1957. It is a mish mash of genres like romance, science fiction and mystery, but the whole book is basically one big propaganda piece for Objectivism. One could say that this started as far back as her book, The Fountainhead, but Atlas Shrugged is arguably the better known one. She also wrote a bunch of non-fiction books about her beliefs, such as The Virtue of Selfishness, but I am assuming that your question refers explicitly to fiction. The reason why her believes are so harmful is basically because it teaches people that it is good to only have your own interests at heart and to avoid altruism altogether because it is harmful. Any rational human being can obviously see the flaws in this philosophy, but I still encounter people who gush about Rand's books where she promotes self-interest above everything else. It's not like her ideas have any merits either, there are many real-world examples of companies that tried to follow her beliefs and it always ended in disaster.

Terry Goodkind is another good example of an author who just can't keep his own warped views out of his books and end up preaching at the readers throughout most of them. Just read the Sword of Truth series for an example of how bad it can get. Not only is Goodkind very anti communism and pro capitalism, but he also appears to hate pacifism and has a huge appreciation of Objectivism. He tries his best to dress up his views in a nice fantasy disguise, but it is impossible to read the books without feeling like the author is trying his best to convince you about his beliefs.

The only other one I can think of right now is Gennady Stolyarov II, with the novel Eden Against The Colossus. It is a science fiction novel that is steeped in Objectivist propaganda. The "hero" of the story is a scientist who discovers a distant planet that is occupied by an alien species unlike anything ever seen before. While observing these aliens, the scientist notices how destructive their nature is and uses it as an opportunity to praise the virtues of Objectivism.

Instead of giving you a list of authors who have strong viewpoints on different things, I will instead present you with something a lot more useful, a list of authors who have deeply misogynistic views. All of them have written the types of books that would give any decent feminist nightmares. However, I think it is important that we are aware of these authors and books, to prevent the rise of this type of view from ever happening again.

Author: Henry Miller - Example of work: Tropic of Cancer. The fact that this book was actually banned at one point because of the obscene language and the obsession the author had with describing all of his sexual escapades should tell you everything you need to know. A lot of the novel is autobiographical, which makes it even more disturbing and if anyone ever had any doubt that Miller was a misogynist, then reading this will quickly cure them of that notion.

Author: J. D. Salinger - Example of Work: The Catcher in the Rye. Many people see this as a beloved "classic" but examining it through a feminist lens reveals that Holden Caulfield is completely incapable of relating to any women. Instead, he either looks down on them or objectifies them. It's easy to ascribe this to the character, but the author also never bothered to write any fleshed out female characters for his books either. It is this that made me scrutinize the author a little closer and discover that he exploited a lot of young women in his time.

Author: Ernest Hemingway - Example of Work: The Sun Also Rises. There's a lot of debate going on about whether Hemingway was actually a sexist, misogynist or if he only pretended to be one. I think the real question should be, is there any difference between the two? Anyway, one only has to look at the way women are portrayed in his books to see what a chauvinist he really was. For further proof of his sexist beliefs, there is a letter that he wrote to his letter, where he not only slanders the sick wife of his friend F. Scott Fitzgerald, but also casually mentions that if a man leaves a woman, he ought to shoot her to save himself trouble, and that it would be worth it even if they hanged you.

Author: Norman Mailer. - Example of Work: The Executioner's Song. It’s clear when reading the novels by Norma Mailer that he had some rather harmful views about women and homosexual people. Reading his book reveals an author who appears to like sexual violence a lot in his stories. It is bad enough that it is clear in his books, but he took things even further in real life. He married something like six times and none of his wives were better off with him. He actually went as far as stabbing Adele, his second wife, with a penknife and nearly killing her in the process. Unbelievably enough, despite only barely missing her heart and shouting at shocked bystanders to leave his wife to die, she did not press charges and he only got a suspended sentence. He also went on to beat his fourth wife and never showed much remorse for any of these actions.

I'm going to go ahead and assume that you mean fiction authors as heaven knows there is no shortage of non-fiction authors who are unable to keep their opinions for themselves. I don't have an issue with authors writing about what they believe in, but if it feels like it is shoehorned in or obvious propaganda in any way, then I'm out. There are plenty of obvious examples of authors who use their writing as a soapbox for their personal views, but I'm more fascinated by books that seemingly contradict their authors. One of my favorite examples is Paradise Lost by John Milton.

I know that Paradise Lost is technically a poem and not a novel, but come on, it spans twelve books, so I'm sure nobody is going to nitpick this factor. For anyone here unfamiliar with their 17th-century poets, Paradise Lost is basically a massive poem about how Adam and Eve were tempted by Lucifer and tricked into the fall of man. Milton's views on the subject couldn't be any clearer, he explicitly states in the first book that it is written with the express purpose of justifying the ways of God to men.

The interesting thing is that despite Milton being a devout Christian and lots of devout Christian readers enjoying the books over the years, it doesn’t appear to be as clear cut when thoroughly examined. Some readers came to the conclusion that instead of the hero being one of the "good" characters, it is actually the "evil" character, Satan, who displays all the characteristics of a hero. It brings up an interesting point about how readers are actually the ones that have ultimate control over the message and viewpoints an author expresses in their books. Perhaps I'm reading too deeply into this whole thing, but it is interesting topic to explore if you are an avid reader.

Another interesting example would be the Harry Potter books by J. K. Rowling. What makes these particular series fascinating is that while very good and quite popular, reading the books doesn't exactly give you any insights into the political leanings of the author. However, we live in the era of social media, so fans have a greater opportunity than ever before to gain insights into the minds of those they admire, which in this case is Rowling. She has made it abundantly clear on social media that her views are very progressive and that she fully supports social justice. It has also resulted in a couple of clashes with some of her readers when she suddenly began to change a couple of things about their back-stories to bring them in line with her views. The books are already written and nothing about them are changed in any way, so one could say that this is an easy way to gain favor and points with the progressive crowd without altering your artistic views or actually changing anything tangible about your existing body of work. I am in no way implying that authors cannot change their views over time or should always be beholden to what they have written in the past, but simply attempting to "rewrite history" so to speak is taking the easy way out.

I could list a couple more examples if anyone is interested in the topic, but I would love to hear what everyone else thinks about this type of phenomena.

One could argue that just about every book ever written incorporates the viewpoint of the author, no matter how unbiased or uninvolved they try to work. Plenty of authors, even some of the big names, have been unable to resist the temptation of creating a protagonist that is just a stand-in for themselves. It is probably a little inevitable that so many protagonists in books are writers themselves because authors stick to the old adage of "write what you know." If you mean more specifically about political or controversial viewpoints that are obvious about the author based on their books, I can think of one or two.

1. Rudyard Kipling ~ The Jungle Book ~ Rudyard Kipling was once seen as one of the greatest writers of his time, but a closer examination of his books in these, shall we say more enlightened times, reveals a author who was deeply cultural insensitive and believed a little too much in British superiority. This is really a pity as there is no doubt that he was a gifted author and many of his books are free of his prejudices or at least contain enough good to overshadow the bad. Unfortunately, he has also written stuff like "The White Man's Burden", which is basically a poem where he revels in the idea of colonialism.

2. H. P. Lovecraft ~ The Call of Cthulhu ~ If you read enough H. P. Lovecraft, you quickly begin to realize that the author was in fact somewhat of a racist. While this is extremely disappointing if you are a fan of his work and very hard to ignore once you notice it in his writing, one has to bear in mind that it was very much the norm for his time. This doesn’t in any way excuse his views, but back in those days, it was probably something that everyone saw as normal and Lovecraft was by no means the only one who was problematic.

3. Ender's Game ~ Orson Scott Card ~ There is still a of debate about this one, but the author of Ender's Game, Orson Scott Card, is an unapologetic homophobe and a lot of people have found his books reflect this viewpoint of his. It's more subtle in some books than others, but still make for uncomfortable reading once it becomes apparent.