Richard Feynman maybe. He was a total genius, and was meant to be an amazing teacher and lots of fun.
Alive: Manuel Castells has done a lot of research on how the internet makes the world a better place. I’ve seen him speak a couple of times and he seems pretty awesome. When you see someone who’s really clever but seems to be a nice guy (/lady) it makes a big difference.
I’d love to meet Ada Lovelace. She worked on the very first ideas about computers and was basically the worlds first programmer. She was also the only legitimate child of Lord Byron, so I’d say her life was quite interesting.
I think I’d probably also have gone for Feynman as well but as I don’t want to pinch Martin’s answer I’ll think of someone else …
I’d quite like to meet Bryan May (astrophysicist and ex lead guitarist from queen), I think Sir Patrick Moor is a pretty funny chap. Some of the most interesting scientists I’ve meet though haven’t been very well known at all.
Alive it would have to be Sir David Attenborough. He was my inspiration as a child and the reason I became interested in the natural world.
Dead I would say it would be Alan Turing. The man was just fascinating. Not only for his amazing contributions to computer science, code breaking and artificial intelligence, but also just his personality and life in general. He never took any credit for his work and was not very outspoken. It would be wonderful to know what was going on in his head.
I think I’d have to meet Niels Bohr, who contributed towards identifying the structure of the atom in the emerging field of Quantum Mechanics. I’ve heard he had a good sense of humour and used to banter with Albert Einstein about his theories.
I think it was Niels Bohr who said “Those who are not shocked by quantum theory do not understand it.”