It showed up out of nowhere, made the most bank in history (for a movie), refused to explain and disappeared for like 15 years, then came back out of nowhere with a sequel movie, a AAA game, and like 3 more movies in the works.
Edit: I think it now has like a Lego line too?
It’s original in the sense that it all started with the movie. There wasn’t any Avatar novels, comic books, toys or video games before the movie.
The story is quite derivative though.