Why some authors sometimes prefer to write fictional novels instead of autobiographies or biographies:
If you meet the requirements for a civil action, you can sue someone for defamation, whether libel or slander, if they have written or said something bad about you. However, you must be able to prove the necessary elements of a defamation suit if you wish to collect damages.
Defamation can take two forms, which are generally referred to as libel and slander. Libel is defined as a defamation of a person, group, organization, product, government, or country that was made in written or printed words or in pictures. Slander is the same thing, except the defamatory statement was made in the form of spoken words, sounds, sign language, or gestures.
More here.