A Not Very Approachable Professor
Another late answer. 

In undergrad, there is a maxim that you should "choose your professors as carefully as your classes." I think in hindsight, most graduates agree with this -- we've all had random classes taught by great professors that were meaningful, while great subjects taught by lousy professors were worthless.

How much more crucial, then, is the choice of your PhD advisor! An advisor in the right area but with the wrong personality is a terrible choice. An advisor in a merely acceptable subfield but the right personality is a much better choice. 

Ideally, you will (a) find someone at your current school who will make a good advisor even if their research area isn't obviously aligned with your current interests, or (b) find that the professor in question is actually reasonable once you get to know him/her. But, I think transferring out would be preferable to working for an unreasonable person -- I've known multiple people who stayed in grad school for 10+ years, and the common problem was an unreasonable advisor.