There are so many people that are eligible for the "smartest person ever" title which makes it very tough on deciding. If I have to pick who was the smartest person ever, I would also have to agree with Medmech's choice of Leonardo Da Vinci. This man was a genius who not only was famous for his artistic works, but also for his scientific and inventions. There are not many who are good at several fields, however, Da Vinci was one of them.