Fan fiction is illegal, or at best in a deeply gray area, it's just that most people realize suing your super-fans is a bad move. There are exceptions of course

Fan fiction is illegal, or at best in a deeply gray area, it's just that most people realize suing your super-fans is a bad move. There are exceptions of course, Anne Rice was famously super litigious over any attempted fan fiction of her characters which generated a lot of bad feelings online. https://www.vice.com/en/article/88gqjz/anne-rice-really-hated-when-people-made-her-characters-bone https://www.vice.com/en/article/88gqjz/anne-rice-really-hate...