We recently received a question about a “Rogue Realm” showing up in the users Cloud account. If you see a Realm that you don’t recognize, it means that you were likely invited to take a training course provided by that user.
As you can see in the screenshot above, I'm the owner of "Ryan's Realm" and I was also invited to take a training course by Rustici Support.
To read more about Realms and how to create them, you can refer to this article: