Other forms: novelists
Someone who writes fictional books is a novelist. If your favorite novelist is Stephen King, it means you're a fan of the horror genre.
When someone writes a novel, a book-length, made-up story, they can describe themselves as a novelist. Some novelists also write non-fiction, poetry, or short stories, and you can also simply call them a "writer" or an "author." Novelist was coined to mean "fiction writer" in the 1720s from novel, though the word existed earlier with several different meanings, including "news-carrier" and "innovator."