Richard Feynman was very smart. He was also a pedantic, so in this 6 minute clip he spends most of the time explaining how a question cannot be answered, while answering that same question more and more precisely:
Feynman was not just smart but also interesting. Not just playing-the-bongos interesting, but in his approach to learning, teaching and exploring.
Having read his autobiographies and learned about his contributions to the field of quantum mechanics, I am reminded of the xkcd strip about the four fundamental forces:
The joke of this is that we all know what gravity is, whereas the other fundamental forces become increasing hard to explain. While on the other hand, physicists know very much about everything but gravity.