Probably someone we have never heard of.
Newton would be a good choice, same for Leonardo De Vinci or maybe Aristotle.
I did once read that some scientists or whatever, have been able to roughly calculate the average IQ of 5th century B.C. citizens of Athens as likely in the 120 range.
Considering the large number of famous people who came from a city of about 100,000 I could see that as true.
Archimedes should be in this conversation.
I would offer Imhotep of Ancient Egypt who invented stone building and set up a medical college that thrived for 2,000 years, giving Egypt the best medical care in the ancient world (average life of an Egyptian was ten years greater than any place else in the Ancient World) He was so beloved by the Egyptians (and Greeks too) that after his death they made him a God. He might not have liked that because he was one of the first to believe there was only one God. A commoner, he became second only to Pharaoh and his good friend too—proving the King was wise enough to place the smartest man in Egypt in control of day by day running of the nation.