Basically any character ever created by Sir Terry Pratchett is hilarious. Honestly, there are just too many to pick from. I'm not kidding, there are thousands of characters spread across the Discworld book, so here are some of my personal favorites:

1. Death - Sir Terry Pratchett is probably the only author ever who could take death and not only turn him into a fully fledged character, but also a very likable one. I just love the way that Death speaks in all caps and the sarcastic way in which he interacts with characters who does stupid things and get to meet him in an untimely manner. Death was such an important character in the Discworld novels that Sir Terry even chose to use him in his final tweets before passing away.

2. Cut-Me-Own-Throat Dibbler - Dibbler is a shady vendor who would do just about anything to hawk his wares. Dibbler doesn't play a very big role in the Discworld universe, but he appears in just about every book and each time he does you are guaranteed some laughs. The way that there is a different "version" of him all over Discworld is also funny as heck.

3. Rincewind - Rincewind appears in a number of Discworld books and he has a streak of bad luck a mile wide. Despite his best efforts to just skate by, Rincewind always gets caught up in situations where his life is in danger. Rincewind is supposed to be a wizard, but doesn't have any type of talent for the magical arts. Rincewind is also very sarcastic and his trusty companion, the "Luggage", is just about the coolest invention in any book, ever.

4. Nobby Nobs - All of the members in the Ankh-Morpork Watch are a hoot, but Cecil Wormsborough St John Nobbs or "Nobby Nobs" as he's known might just be the funniest. Nobby is supposed to be a human, but has to carry around papers to prove it because of his monkey-like appearance. Despite his occupation Nobby has a habit of "collecting" things that doesn't belong to him and he is actually a lot smarter than what he looks.

5. Granny Weatherwax - Granny Weatherwax is one of the many witches in the Discworld novels and such a terror or broom that apparently the flight migration patterns of an entire continent changed to avoid her. Granny is such an imposing character that the trolls know her as "She Who Must be Avoided" and in Dwarfish she is called "Go Around The Other Side of The Mountain."

Voracious readers probably have a larger pool to pick from but I have been working my way through the classics, so here are my top picks.

-Major Major from Catch 22 by Joseph Heller.
-Holden Caulfield from The Catcher in the Rye by J. D. Salinger.
-Anne Shirley from Anne of Green Gables by L. M. Montgomery.
-Bertie Wooster from The Jeeves and Wooster books by P. G. Wodehouse.
-Ignatius J. Reilly from A Confederacy of Dunces by John Kennedy Toole.
-Don Quixote from Don Quixote by Miguel de Cervantes.
-Frieda Wentworth from At Freddie's by Penelope Fitzgerald.

If you enjoy British humor, which to be honest is mostly snark and sarcasm, then you will love the character of Arthur Dent in The Hitchhiker's Guide to the Galaxy. Forget the movie, it does a pretty poor job of capturing the wit and weary resignation of Arthur as he finds himself not only losing his house, but also his planet when some aliens decide Earth is in the way of their hyperspace bypass. This is just the beginning of his adventures and his comments and reactions to the absurdity of the situations that he finds himself in kept me laughing throughout the books. Douglas Adams had a definite knack for funny characters and it's not just Arthur who can make you laugh, but also the rest of the cast, especially Ford Prefect, Zaphod Beeblebrox and Marvin the Paranoid Android.

Is there really a thing such as a funniest character in literature? Plenty of characters in books have made me laugh out loud, but so have many people in reality and I wouldn't consider any of them to be the funniest. A character that just tries to be funny all the time is going to be like a clown and not very useful for the progression of the story. Books should include humor sure, but characters that are just funny all the time will be too one dimensional.

I have found that comedy is unfortunately one of the things that become very dated in literature, especially when authors try to incorporate elements of what is funny at the time of writing. Of course there are exceptions to this, but in general characters who may have been laugh out loud funny in their time now just come across as shallow or dated.

I haven't read nearly enough books to conclusively answer this, but from all the books that I have read there is one character that stands out. His name is Rincewind and he can be found in a number of the Discworld novels by British author, Terry Pratchett. Rincewind is a wizard, but not a very good one and flunked out of the Unseen University if I remember correctly. The only skills Rincewind seems to possess is the ability to turn just about any situation into a catastrophe and then run away from the people who inevitably want to kill him. Rincewind isn't actually the bumbling fool that he and everyone around him believes he is, but that just makes the situations that he finds himself in even funnier. Rincewind isn't in all of the books, so read The Colour of Magic, The Light Fantastic, Sourcery, Eric, Interesting Times, The Last Continent and The Last Hero to follow his adventures.