Often when our brainy, busy clients first discuss blogging they will refer to a famous example in their particular field. So maybe Joe Pulizzi in marketing or Tomasz Tunguz in VC.
The danger is that they are very likely discussing someone who is actually a professional communicator and not really a VC or an at-the-coal-face marketer. They are often writing and giving speeches and blogging, tweeting pretty much full-time and in that sense they are not very useful role-models for our users.
The diagram (and linked article) below has a rather nice way of looking at these issues for the domain experts.
Expert: someone who demonstrates their knowledge on a specific topic, creating new insights in their domain of expertise. This is the “subject-matter expert” who often writes blog posts, is active on social media, and is regarded as an authority in the work place.