There are quite a number of examples of characters in books
which the authors of the series eventually hated them, but was forced to keep on living with them due to pressure from fans
, or from the publisher
The most famous examples I've heard of are Sherlock Holmes and James Bond.
Sherlock Holmes was killed (murdered, some would say) by his creator, Sir Arthur Conan Doyle . This loss was taken so seriously that the staff of the London paper where the stories were published took to wearing black arm-bands, as a sign of grief. Eventually, the author was forced to bring him back to life, using some kind of flimsy excuse for his survival. (dreamtimer says that one reader of holmes serials was said to have written to doyle with the opening line "you beast!"...)
Something similiar happened with James Bond, who was also killed by his creater, Ian Fleming. This time, the publishers (who were getting fat on the revenues from the series) pressured the author into bringing the suave, martini-drinking hero back from the dead.
There are more cases like those, but they tend to be more obscure. The two listed above are probably the most famous. But don't worry, other authors have seen this happen, and took notice. Most notable is probably the Sten series, which the authors (Alan Cole and Chris Bunch) limited themselves to about 1,000,000 words -- so they wouldn't keep writing, and wouldn't have to kill the hero.