Stephen Hawking is a British physicist (author of Brief History of Time) who has Motor Neuron Disease. He is confined to a wheelchair, can't even speak and can only move two fingers. He communicates with the help of his computer. I think the fact that he can pursue theoretical physics despite all this is really really admirable.
Having said that however, one must also realize that the kind of hype that surrounds him is not really justified. It is not valid to call him the greatest scientist after Einstein, or compare him to Newton. There are lots of people who have done more work than he has, and after all he hasn't even got the Nobel prize. While he must be appreciated, we must not get carried away by the media which as usual has tremendous exaggerating capabilities.