It was a collective effort by internet users. There wasn't a single person who can be credited with inventing them. They sort of emerged organically in online communities.
The origin of fiction is not something that can be precisely dated. It developed throughout history as people's creativity and desire to tell made-up tales grew. Different cultures likely had early forms of fiction at various points.
The invention of novels is a gradual process that can't be tied to a specific moment. They developed from earlier forms of storytelling throughout history.