Heard an old joke about someone trying to namedrop. The person they were talking to didn't know who they were talking about, so they said, "Well, they really are very famous, even though most people don't know who they are."
But there's a kernel of truth in that old joke, namely that someone not all that well known can still be very influential, though they are by definition not very famous. Further, certain people really like the idea of knowing people like this, since it makes them feel like they are "in the know". I'm not talking about conspiracy theories, like the Head of the Bilderbergers or Masons or something. I mean, perhaps there is some fashion designer that fashion designers are all copying, or some music mogul who pretty much decides what the next pop music style is going to be. And then the internet is rife with urban legends of people who can build up a product's brand through anonymous viral marketing.
Is there a single word for people, organizations, what have you, that fit this description?