Lady Diana. I want to tell her how much she is admired around the world for her beauty & character and how she is missed after her death. I want to ask her why the heck did she marry Prince Charles and if she is happy about William marrying Kate.
I would meet Johnny Depp or Kobe Bryant and I will say to Johnny, you rock but how you got so famous. I ask Kobe you rock at basketball and I want to be just like you in basketball cause I suck in basketball :P
It is without any doubt in the world (assuming in your scenario I can speak with people from history) Harriet Tubman...of the Underground Railway before the Civil War...escaped from slavery herself and then went BACK until she had gotten several hundred more people.
Clearly one of the most courageous human beings who ever lived, and what I would say is Thanks.