There are many who say that the smartest man to have ever lived was Albert Einstein. He is certainly one of the most famous of the great thinkers and his intellect contributed massively to the advancement of science. He must rank as one of the smartest people around
For those who want a more measurable answer based purely on measured intelligence, Einstein's massive IQ of 160 is high indeed, but there are quite a few others who are/was much smarter.
Kim Ung-young, A South Korean born man, At the age of 7 he was invited to America by NASA ,finished his university studies, eventually getting a PhD. in physics at Colorado State University before he was 16, Has a Outstanding IQ of 210-215. To the best of my knowledge he would be the smartest person who has lived to date.