What's your thing?

I've noticed that most of the people who have large followings on the internet (OK, I mean Twitter, because it's really easy to count), have a thing. Sure, many people are popular because they're famous (Ashton, LeVar, Oprah, etc), but all the others have grown a large following by picking something and owning it. 

In other words, niche is the new big. 

It's too bad for me because I don't have a well defined thing. I work in marketing, conferences, social media, consulting, and of course, I write, but none of that is really my thing.

What about you? What's your thing? Has it built you an audience?