First, it's Grigori (Григорий) or "Grisha" for short. Secondly, there's quite a few mathematicians that have that look. I remember a funny story one of my professors told me about Campus Security not allowing him into a building because they thought he was a homeless person trying to get some food, before another professor called out his name and explained that he was, in fact, an eminent professor in the Math department.

That said, I sometime feel this way when I run into a professor on the BART or something. "Doesn't anybody realize they're in the presence of a genius?"