Are you aware that he is almost completely paralysed? Stuck in a body he can't move?
Do you know what death is like for someone with motor neurone disease? I'm not going to describe it here, because it is far too distressing. Suffice to say, his condition, and the death at the end of it, are horrifying. The worst part is that up until his early twenties he had no symptoms. Motor neurone disease can affect any of us, symptoms can come on suddenly and without warning.
Maybe you should look it up, before you start making jokes about his condition.
I agree totally with most of the other answers wondering why you would even think of asking this. What a cruel and ignorant question! Dr. Hawking is probably the most brilliant mind in theoretical physics today, trapped in a body that will not obey that mind. Even so, his accomplishments dwarf those of most able bodied individuals. Most of us could only hope to achieve a tenth of what he has!
I hope you never suffer yourself, or have to watch anyone you care about, suffer from a condition such as his. Right now you don't sound smart, funny or clever, but incredibly childish, cruel and pathetic. Do you really have nothing better to do with your time than make jokes at the expense of others and their disabilities?
His condition is horrendous for anyone to have to suffer from. His inevitable death from that degeneration will not be pleasant and will probably not be swift. For living as he does he deserves not only respect and sympathy but admiration for maintaining his sense of humour and getting on with his life as best he can. You, frankly, deserve very little in the way of any of those things right now.
Of course he's a real person. He's ill, & suffers from a very cruel, debilitating disease. Even with all he has to deal with, he has developed a brilliant intellect & has contributed more to the science of theoretical cosmology than anyone since Einstein. Take the time to read about his life & accomplishments at the link below.
You should HOPE to accomplish one tenth of what he has in your lifetime.