Terry Pratchett

Sir Terry Pratchett is a wonderful writer, entertaining person and fascinating thinker. He gave a recent lecture (broadcast on the BBC) entitled Shaking Hands with Death (readers of his Discworld books will see the funny side of this). It was an interesting addition to the debate on assisted suicide. Pratchett was diagnosed with a form of early onset Alzheimer's, which is slowly diminishing his mental prowess and changing his ability to continue doing what he does best, writing witty, insightful and at times completely bonkers books. (I recommend everyone reads Nation, it's wonderful stuff). There's an extract of his talk here. But I recommend you take an hour to watch him make his case.
 Not only am I a huge fan of his books, I once had the honour of meeting him when The Amazing Maurice and his Educated Rodents was nominated for the Carnegie award (which it won). In person he is funny, intelligent, wry and friendly. And yes, he always wears that hat.
His website is here.