His writings were so brilliant, particulalry Critique of Pure Reason, that folks that didn't understand it at first had to take multiple attempts at interpreting it, correcting themselves, and reinterpreting it before they got the point amd acceded he was correct in the end. If there had been no Kant, it may have taken longer to get a Russell, and therefore a much delayed Wittgenstein, Turing....... And therefore would likely not have entered the digital age for some time..... Though I digress....

How can one say. What one person prefers another doesn't, and how would you measure being smart, what is the scale? They all have something to add, something to say and make our lives more interesting, more enjoyable, more magical.

Socrates Plato was his student

Socrates because he started it all and Plato learned from him..

Thales father of all Materialists, Atheists and scientists....poor list to choose from ....Nietzsche was not very optimistic....we are in our 27th century of Atheism because of Thales

Wittgenstein is my favorite. Then Marx, then Hegel and Nietzsche. But "smartest" is too vague.

"I know that I am intelligent, because I know that I know nothing."

Socrates

"I am the wisest man alive, for I know one thing, and that is that I know nothing."

Socrates

Am I the only one who just sang Bruces' Philosophers' Song from Monty Python?

I’m not sure who was the smartest, as both Plato and Aristotle were two of the greatest geniuses of all time. I voted for Aristotle because of his contributions to science and logical thinking in general.

Id go with Aristotle - although im no expert on the topic.