In the Middle-earth universe, there are a handful of wizards who work in various ways to fight evil. Out of universe, we know these wizards to be Istari, Maia who are in Middle-earth working to defeat Sauron, and we know this thanks to The Silmarillion which explains the origins of Middle-earth.
In universe though, I'd expect this sort of knowledge to be pretty rare. Do we know how rare it is? Who in Middle-earth knows that these wizards are Istari, and the ramifications of this? I'm not looking for a list of specific individuals here, I seek more a list of groups of people.
For example, I'd expect the Noldor who remain in Middle-earth to know what's up with the Istari, since it's part of their personal past. But do any dwarves know? Do any humans? What about Rohan's royalty? The Stewards of Gondor?