I'd be inclined to nominate Einstein as the most intelligent non-living person, and Stephen Hawking as the most intelligent person living, but measuring intelligence is very difficult - accademic intelligence is not eh only measurable form, and IQ Tests only tend to prove that you can do IQ Tests, so it does come down to opinion, and I think most of the people who think about it would probably offer the same names as i have - but you may find differences here on the site.