Thats a really good question.
I'm not really sure about who I would meet, as there are several.
Robert Oppenheimer- ask him about the work on the manhattan project (atom bomb-1945) and how his own conscience collided with the demands from the US government. He also worked with some now-famous names such as Rutherford and Bohr.
Marie Curie- Her dedication during her PhD was phenomenal, she rarely even stopped to eat as she was so into her work.
Bin Laden- just to give him a kicking
others include-
Sir Alex Ferguson, George Best, keira Knightley (so fit!!!), Guy Fawkes, William Shakespeare, Kurt Cobain.
There are more but the first two and Kurt Cobain are the ones I would most like to meet.