Present, my vote goes to Penrose.

We don't have sufficient information to speak to the majority of mankind, so it's really not a meaningful question.

(http://www.autoadmit.com/thread.php?thread_id=5746210&forum_id=2#49072538)

Newton, Gauss amd Leibniz all strong contenders over Feynman, I think

(http://www.autoadmit.com/thread.php?thread_id=5746210&forum_id=2#49072543)

I really don't know anything Eastern, so my response to this question eliminates the majority of people right off the bat due to my own ignorance.

(http://www.autoadmit.com/thread.php?thread_id=5746210&forum_id=2#49072546)

Both Tao and Witten are American mathematicians

(http://www.autoadmit.com/thread.php?thread_id=5746210&forum_id=2#49072552)

I'd argue even the likes of Newton or Leibniz are too old to speak of in the same way as modern people.

I actually don't know much about Witten. I bet most scientists don't have Feynman's charisma & ability to communicate, though. (Just flip through anything Penrose has written.)

(http://www.autoadmit.com/thread.php?thread_id=5746210&forum_id=2#49072579)

(http://www.autoadmit.com/thread.php?thread_id=5746210&forum_id=2#49075386)

But newton was probably smarter.

(http://www.autoadmit.com/thread.php?thread_id=5746210&forum_id=2#49075449)

There were also great contributions from India & the far East in classical & medieval times that most of us aren't aware of. (How many of us could name the author of Al-Jabr, let alone read it?)

We can speak of those the knowledge of whom is extant, or has been translated into our native language, but not so much to the 'most intelligent person ever.'

(http://www.autoadmit.com/thread.php?thread_id=5746210&forum_id=2#49076775)

I would argue that the most influential individuals aren't necessarily the most intelligent. The further back in time we go, the more influential an individual becomes. Some kid in 2021 with a wacky GUT hasn't had 2.5k years to gain the infamy of a Plato.

Besides, could Plato even handle UG physics at CalTech today? (Conversely, could a CalTech grad today do what Plato did c. 500 BCE?)

Obviously, OP's question has no absolute answer, but it's still fun to argue.

(http://www.autoadmit.com/thread.php?thread_id=5746210&forum_id=2#49077202)

The only other contender is Einstein, who on 2 occasions figured out things in physics that don't make intuitive sense at all.

(http://www.autoadmit.com/thread.php?thread_id=5746210&forum_id=2#49075462)

Tesla, Newton, Da Vinci, Plato

(http://www.autoadmit.com/thread.php?thread_id=5746210&forum_id=2#49075746)

As much as I hate to nominate a turd, Ramanujan is easily a top contender

(http://www.autoadmit.com/thread.php?thread_id=5746210&forum_id=2#49076800)

contemporary and sometimes-colleague of newton iirc

(http://www.autoadmit.com/thread.php?thread_id=5746210&forum_id=2#49077075)