Well, there wasn't any "need". There isn't a "need" for anyone to invent any character. It is a story, she invented a story, and you don't need reasons to do that.
JK Rowling is a successful author who does not need a job (other than writing) because she has so much money from writing the Harry Potter series.
"Bone of the father, unknowingly given", "Flesh of a servant, willingly given", and blood of an enemy (but I forget the quote for that one). Sources: Harry Potter and the Goblet of Fire by JK Rowling
Contrary to the the studios claim J.K. Rowling DOES appear in the second film as an uncredited professor at the head table. Unfortunately sometimes on the Internet people sometimes do no research before they attempt to correct answers that do not need to be corrected. The answer below was erroneously placed here to perpetuate the myth that J.K.Rowling did not appear in any of the films. This of course is false and can be discovered if only you seek the answer. "No. It has been said the director asked JK Rowling if she wanted to be Harry's mother in the Sorcerer's Stone movie, but she said no because she thought she would mess it up somehow." This answer is based on speculation and has no real merit in the face if the visual evidence. See for yourself. http://www.facebook.com/media/set/?set=a.230110833743218.58226.100002329104960&type=3#!/photo.php?fbid=230110837076551&set=a.230110833743218.58226.100002329104960&type=3&theater
An author.It was the only thing she really wanted to do.
Harry potter in a flashforward scene.
J.K Rowling has the rights to the Harry Potter series. She has not allowed them to be published in e-book form which means any form of the Harry Potter books online is illegal and should not be trusted due to security risks.
There are many Harry Potter RPGS (virtual games) out there. All you need to do is preform a search.
Since the Harry Potter series is set in a fictional world, it doesn't really need to be researched because everything is made up by J.K. Rowling. Similarly, Twilight also features fictional vampires (although is set in the 'real world') which, although different from traditional vampires, are made up by Stephanie Meyer.
A lot of them are based on Latin words, such as Expecto Patronum, which is derived from the Latin words expeto, meaning to desire or be in need of, and patronus, meaning protector.
Extras.
um because its a story like Harry Potter, don't need proof that Harry Potter ain't real
J.K. Rowling typically earned royalty rates ranging from 8% to 15% of the cover price for the Harry Potter books, depending on the format and sales volume. However, with her considerable success and negotiating power, she may have secured more favorable terms in certain cases.