Who (if anyone) can add canon to an existing universe?

Question

Under normal circumstances, it's obvious that the original writer would be in control of the canon, but what about when the IP-owner is deceased or no longer participating in their industry? This applies to anything requiring writing, be it fiction novels, game stories, movies, what-have-you.

For example, Tolkein fleshed out a huge and detailed universe in his works. There's plenty there to draw from for everything from more novels, to games, and movies. But at what point are writers crossing from canon to non-canon? Was the universe ever "passed on" to someone who is in charge of it now? Is that even possible? Or is every derivative of his works just that: a derivative?

In the reverse, you could take the Battletech franchise. It was designed and written as a game, but then became popular enough to spawn a sizable amount of novels and video games. But who is considered to be the IP-owner that can say "Yes this is part of the universe" and "No that's not possible"? Or is there even such a person/group?

Answer 1

I would have to think that's different for each instance/author/book series.

IIRC, Isaac Asimov started the "Robot City" series, then intentionally let little known writers expand upon it under his name, which I believe his wife carried on after he passed away. (It's been many years since I read up on this, so I could be off on the details.)

They were published as "Isaac Asimov's Robot City", with the actual author in much smaller lettering. This was to give the appearance that it was Asimov's work, with the intention of giving actual experience (and money) to writers that needed the attention of readers (and publishers). I believe that the books not written by Asimov, in this case, would have been canon for the series.

This is not the norm, of course, so you're going to have to research who has the copyright and to ask their permission. If no one owns the copyright, I'm not sure how the "canon" would work there.