I saw Stephen Hawking in college. He gave a basic physics lecture to the audience, although at the time I didn't know as much as I do now so it was pretty cool stuff then.
It was painstaking watching him answer questions from the audience. Took forever for him to get out his answers, but even then he was funny and charismatic and darned if he didn't captivate all of us.
The world owes so much to him. Einstein may have predicted black holes, but it was Stephen who gave us Hawking radiation (who would've guessed that Stephen Hawking would've discovered Hawking radiation?).
It's too bad he didn't survive to see quantum mechanics and general relativity married.
The world is a lesser place without him, although I'll take solace knowing that matter/energy is neither created nor destroyed.