I think Stephen Hawking's is up there on my list of smart people
Marie Curie has to be up there.
Marilyn Vos Savant
Ever heard of would be Nikola Tesla. Albert Einstein was once asked what it was like to be the smartest man on Earth. His response was he didn't know. Go ask Nikola Tesla.
Another one I would say is Leonardo Da Vinci.
Know personally, probably my dad. He could see things in ways most people couldn't. He seemed to understand the science behind everything. He thought things through and taught his kids to do the same. We were never just given the answer if we had a question. He helped or had us figure it out, or look it up. And we didn't have Google. We used the encyclopedia or the library.