The first big celebrity to post videos on YouTube was Oprah Winfrey.

YouTube was still a new site with a close community where most people knew most of the big names on there. That changed when Oprah joined. Same thing will probably happen here.

You can read my reporting of this, here:
http://youtubestars.blogspot.com/2007/11/oprah-is-on-youtube.html

To answer your question, someone most people admire, like maybe Kate Middleton, Duchess of Cambridge.